Under-LCD screen optical sensor module for on-screen fingerprint sensing

ABSTRACT

Devices and optical sensor modules are provided for provide on-screen optical sensing of fingerprints by using a under-screen optical sensor module that captures and detects returned light that is emitted by a LCD display screen for displaying images and that is reflected back by the top surface of the screen assembly.

CROSS REFERENCE TO RELATED APPLICATIONS

This patent document claims the benefits and priorities of U.S.Provisional Patent Application No. 62/396,153, filed on Sep. 17, 2016;U.S. Provisional Patent Application No. 62/412,777, filed on Oct. 25,2016; and U.S. Provisional Patent Application No. 62/468,337, filed onMar. 7, 2017.

This patent document also claims the benefits and priority of, and is acontinuation-in-part application of, U.S. patent application Ser. No.15/616,856, filed on Jun. 7, 2017, which claims the benefits andpriorities of U.S. Provisional Patent Application No. 62/347,073, filedon Jun. 7, 2016; U.S. Provisional Patent Application No. 62/363,832,filed on Jul. 18, 2016; and U.S. Provisional Patent Application No.62/363,823, filed on Jul. 18, 2016. In addition, U.S. patent applicationSer. No. 15/616,856 claims the benefits and priority of, and is acontinuation-in-part application of, U.S. patent application Ser. No.15/421,249, filed on Jan. 31, 2017, which claims the benefits andpriorities of U.S. Provisional Patent Application No. 62/289,328, filedon Jan. 31, 2016; U.S. Provisional Patent Application No. 62/330,833,filed on May 2, 2016; and U.S. Provisional Patent Application No.62/347,073, filed on Jun. 7, 2016. Furthermore, U.S. patent applicationSer. No. 15/616,856 claims the benefits and priority of, and is acontinuation-in-part application of, International Patent ApplicationNo. PCT/US2016/038445, filed on Jun. 20, 2016, which claims the benefitsand priority of U.S. Provisional Patent Application No. 62/181,718,filed on Jun. 18, 2015.

This patent document also claims the benefits and priority of, and is acontinuation-in-part application of, U.S. patent application Ser. No.15/421,249, filed on Jan. 31, 2017, which claims the benefits andpriorities of U.S. Provisional Patent Application No. 62/289,328, filedon Jan. 31, 2016; U.S. Provisional Patent Application No. 62/330,833,filed on May 2, 2016; and U.S. Provisional Patent Application No.62/347,073, filed on Jun. 7, 2016. In addition, U.S. patent applicationSer. No. 15/421,249 claims the benefits and priority of, and is acontinuation-in-part application of, International Patent ApplicationNo. PCT/US2016/038445, filed on Jun. 20, 2016, which claims the benefitsand priority of U.S. Provisional Patent Application No. 62/181,718,filed on Jun. 18, 2015.

This patent document also claims the benefits and priority of, and is acontinuation-in-part application of, International Patent ApplicationNo. PCT/US2016/038445, filed on Jun. 20, 2016, which claims the benefitsand priority of U.S. Provisional Patent Application No. 62/181,718,filed on Jun. 18, 2015.

This patent document also claims the benefits and priority of, and is acontinuation-in-part application of, International Patent ApplicationNo. PCT/CN2016/104354, filed on Nov. 2, 2016, which claims the benefitsand priority of U.S. Provisional Patent Application No. 62/249,832,filed on Nov. 2, 2015.

The entire contents of the before-mentioned patent applications areincorporated by reference as part of the disclosure of this document.

TECHNICAL FIELD

This patent document relates to optical sensor modules capable ofperforming one or more sensing operations such as fingerprints or otherparameter measurements based on optical sensing in an electronic devicesuch as a mobile device or a wearable device or a larger system.

BACKGROUND

Various sensors can be implemented in electronic devices or systems toprovide certain desired functions.

A sensor that enables user authentication is one example of such sensorsfor devices including portable or mobile computing devices (e.g.,laptops, tablets, smartphones), gaming systems, various databases,information systems or larger computer-controlled systems can employuser authentication mechanisms to protect personal data and preventunauthorized access. User authentication on an electronic device can becarried out through one or multiple forms of biometric identifiers,which can be used alone or in addition to conventional passwordauthentication methods. A popular form of biometric identifiers is aperson's fingerprint pattern. A fingerprint sensor can be built into theelectronic device to read a user's fingerprint pattern so that thedevice can only be unlocked by an authorized user of the device throughauthentication of the authorized user's fingerprint pattern. Anotherexample of sensors for electronic devices or systems is a biomedicalsensor, e.g., a heartbeat sensor in wearable devices like wrist banddevices or watches. In general, different sensors can be provided inelectronic devices to achieve different sensing operations andfunctions.

Fingerprints can be used to authenticate users for accessing electronicdevices, computer-controlled systems, electronic databases orinformation systems, either used as a stand-alone authentication methodor in combination with one or more other authentication methods such asa password authentication method. For example, electronic devicesincluding portable or mobile computing devices, such as laptops,tablets, smartphones, and gaming systems can employ user authenticationmechanisms to protect personal data and prevent unauthorized access. Inanother example, a computer or a computer-controlled device or systemfor an organization or enterprise should be secured to allow onlyauthorized personnel to access in order to protect the information orthe use of the device or system for the organization or enterprise. Theinformation stored in portable devices and computer-controlleddatabases, devices or systems, may be personal in nature, such aspersonal contacts or phonebook, personal photos, personal healthinformation or other personal information, or confidential informationfor proprietary use by an organization or enterprise, such as businessfinancial information, employee data, trade secrets and otherproprietary information. If the security of the access to the electronicdevice or system is compromised, these data may be accessed by others,causing loss of privacy of individuals or loss of valuable confidentialinformation. Beyond security of information, securing access tocomputers and computer-controlled devices or systems also allowsafeguard the use of devices or systems that are controlled by computersor computer processors such as computer-controlled automobiles and othersystems such as ATMs.

Security access to a device such as a mobile device or a system such asan electronic database and a computer-controlled system can be achievedin different ways such as use of user passwords. A password, however,may be easily to be spread or obtained and this nature of passwords canreduce the level of the security. Moreover, a user needs to remember apassword to use electronic devices or systems, and, if the user forgetsthe password, the user needs to undertake certain password recoveryprocedures to get authenticated or otherwise regain the access to thedevice and such processes may be burdensome to users and have variouspractical limitations and inconveniences. The personal fingerprintidentification can be utilized to achieve the user authentication forenhancing the data security while mitigating certain undesired effectsassociated with passwords.

Electronic devices or systems, including portable or mobile computingdevices, may employ user authentication mechanisms to protect personalor other confidential data and prevent unauthorized access. Userauthentication on an electronic device or system may be carried outthrough one or multiple forms of biometric identifiers, which can beused alone or in addition to conventional password authenticationmethods. One form of biometric identifiers is a person's fingerprintpattern. A fingerprint sensor can be built into an electronic device oran information system to read a user's fingerprint pattern so that thedevice can only be unlocked by an authorized user of the device throughauthentication of the authorized user's fingerprint pattern.

SUMMARY

Optical sensor modules can be placed under liquid crystal display (LCD)screens to provide optical sensing functions including opticalfingerprint sensing. In some implementations, optical sensing isprovided for determining whether an object in contact is from a liveperson.

In one aspect, the disclosed technology can be used to construct anelectronic device capable of detecting a fingerprint by optical sensingto include a liquid crystal display (LCD) screen that provides touchsensing operations and includes a LCD display panel structure to displayimages; a top transparent layer formed over the device screen as aninterface for being touched by a user for the touch sensing operationsand for transmitting the light from the display structure to displayimages to a user; and an optical sensor module located below the displaypanel structure to receive probe light that passes through the LCDscreen to detect a fingerprint, wherein the optical sensor moduleincludes an optical collimator array of optical collimators thatreceives the probe light and an optical sensor array of optical sensorsto receive the probe light from the optical collimator array.

In another aspect, the disclosed technology can be used to construct anelectronic device capable of detecting a fingerprint by optical sensingthat includes (1) a liquid crystal display (LCD) screen that providestouch sensing operations and includes a LCD display panel structure todisplay images; a LCD backlighting light module coupled to the LCDscreen to produce backlighting light to the LCD screen for displayimages; (2) a top transparent layer formed over the device screen as aninterface for being touched by a user for the touch sensing operationsand for transmitting the light from the display structure to displayimages to a user; (3) an optical sensor module located below the LCDdisplay panel structure to receive probe light that is reflected fromthe top transparent layer and passes through the LCD screen to detect afingerprint; (4) one or more probe light sources, separate from the LCDbacklighting light module, located under the LCD display panelstructure, to produce the probe light that passes through the LCDdisplay panel structure to illuminate a designated fingerprint sensingarea on the a top transparent layer to be visibly different from asurrounding area of the top transparent layer for a user to place afinger for optical fingerprint sensing; and (5) a device control modulecoupled to the optical sensor module to process an output of the opticalsensor module to determine whether a detected fingerprint by the opticalsensor module matches a fingerprint an authorized user, in addition todetecting fingerprints, also detect a biometric parameter different forma fingerprint by optical sensing to indicate whether a touch at the toptransparent layer associated with a detected fingerprint is from a liveperson.

In yet another aspect, the disclosed technology can be used to constructan electronic device capable of detecting a fingerprint by opticalsensing to include a liquid crystal display (LCD) screen that providestouch sensing operations and includes a LCD display panel structure todisplay images; a LCD backlighting light module coupled to the LCDscreen to produce backlighting light to the LCD screen to displayimages; a top transparent layer formed over the LCD screen as aninterface for being touched by a user for the touch sensing operationsand for transmitting the light from the display structure to displayimages to a user; and an optical sensor module located below the LCDpanel structure to receive light returned from the top transparent layerto detect a fingerprint. The optical sensor module includes atransparent block in contact with the display panel substrate to receivethe light from the display panel structure, an optical sensor array thatreceives the light and an optical imaging module that images thereceived light in the transparent block onto the optical sensor array.One or more probe light sources, separate from the LCD backlightinglight module, are located under the LCD display panel structure, toproduce the probe light that passes through the LCD display panelstructure to illuminate a designated fingerprint sensing area on the atop transparent layer to be visibly different from a surrounding area ofthe top transparent layer for a user to place a finger for opticalfingerprint sensing.

The drawings, the description and the claims below provide a moredetailed description the above and other aspects, their implementationsand features of the disclosed technology.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an example of a system with a fingerprintsensing module which can be implemented to include an opticalfingerprint sensor disclosed in this document.

FIGS. 2A and 2B illustrate one exemplary implementation of an electronicdevice 200 having a touch sensing display screen assembly and an opticalsensor module positioned underneath the touch sensing display screenassembly.

FIGS. 3A and 3B illustrate an example of a device that implements theoptical sensor module in FIGS. 2A and 2B.

FIGS. 4A and 4B show an example of one implementation of an opticalsensor module under the display screen assembly for implementing thedesign in FIGS. 2A and 2B.

FIGS. 5A, 5B and 5C illustrate signal generation for the returned lightfrom the sensing zone on the top sensing surface under two differentoptical conditions to facilitate the understanding of the operation ofthe under-screen optical sensor module.

FIGS. 6A-6C, 7, 8A-8B, 9, and 10A-10B show example designs ofunder-screen optical sensor modules.

FIG. 11 shows imaging of the fingerprint sensing area on the toptransparent layer via an imaging module under different tilingconditions where an imaging device images the fingerprint sensing areaonto an optical sensor array and the imaging device may be opticallytransmissive or optically reflective.

FIG. 12 shows an example of an operation of the fingerprint sensor forreducing or eliminating undesired contributions from the backgroundlight in fingerprint sensing.

FIG. 13 shows a process for operating an under-screen optical sensormodule for capturing a fingerprint pattern.

FIGS. 14, 15 and FIG. 16 show an example of an operation process fordetermining whether an object in contact with the LCD display screen ispart of a finger of a live person by illuminating the finger with lightin two different light colors.

FIGS. 17A-17B, 18 and 19A-19C show optical collimator designs foroptical fingerprint sensing suitable for implementing the disclosedunder-screen optical sensor module technology.

FIGS. 20, 21A, 21B, 22A, and 22B illustrate examples of various designsfor fingerprint sensing using a under-screen optical sensor module usingan array of optical collimators or pinholes for directing signal lightcarrying fingerprint information to the optical sensor array.

FIGS. 23 and 24 show examples of under-screen optical sensor moduleswith optical collimators.

FIG. 25 shows an example an optical collimator array with opticalfiltering to reduce background light that reaches the photodetectorarray in the under-screen optical sensor module.

FIGS. 26A, 26B, 27 and 28 show examples of optical collimator designsfor the optical sensing under the LCD display screen.

FIGS. 29, 30 and 31 illustrate improved optical imaging resolution basedon a pinhole camera effect in designing the optical sensor module.

FIG. 32 shows an example of an under-LCD optical sensor module using anoptical pinhole array for optical sensing.

FIGS. 33A and 33B show an example of an optical fingerprint senor undera LCD display panel having an optical deflection or diffraction deviceor layer.

FIGS. 34A, 34B and 34C show examples of LCD diffuser designs forimproved under-LCD optical sensing.

FIGS. 35A and 35B show examples of LCD reflector designs for improvedunder-LCD optical sensing.

FIG. 36 shows an example of a LCD light source design for improvedunder-LCD optical sensing.

FIGS. 37A-37D show examples of enhancement features for improvedunder-LCD optical sensing.

FIG. 38 shows an example of a LCD waveguide design for improvedunder-LCD optical sensing.

FIGS. 39A-39C show examples of LCD backlighting light source andillumination light source for improved under-LCD optical sensing.

FIG. 40 shows two different fingerprint patterns of the same fingerunder different press forces: the lightly pressed fingerprint and theheavily pressed fingerprint.

DETAILED DESCRIPTION

Electronic devices or systems may be equipped with fingerprintauthentication mechanisms to improve the security for accessing thedevices. Such electronic devices or system may include, portable ormobile computing devices, e.g., smartphones, tablet computers,wrist-worn devices and other wearable or portable devices, largerelectronic devices or systems, e.g., personal computers in portableforms or desktop forms, ATMs, various terminals to various electronicsystems, databases, or information systems for commercial orgovernmental uses, motorized transportation systems includingautomobiles, boats, trains, aircraft and others.

Fingerprint sensing is useful in mobile applications and otherapplications that use or require secure access. For example, fingerprintsensing can be used to provide secure access to a mobile device andsecure financial transactions including online purchases. It isdesirable to include robust and reliable fingerprint sensing suitablefor mobile devices and other applications. In mobile, portable orwearable devices, it is desirable for fingerprint sensors to minimize oreliminate the footprint for fingerprint sensing given the limited spaceon those devices, especially considering the demands for a maximumdisplay area on a given device.

The light produced by a display screen for displaying images necessarilypasses through the top surface of the display screen in order to beviewed by a user. A finger can touch the top surface and thus interactswith the light at the top surface to cause the reflected or scatteredlight at the surface area of the touch to carry spatial imageinformation of the finger to return to the display panel underneath thetop surface. In touch sensing display devices, the top surface is thetouch sensing interface with the user and this interaction between thelight for displaying images and the user finger or hand constantlyoccurs but such information-carrying light returning back to the displaypanel is largely wasted and is not used in most touch sensing devices.In various mobile or portable devices with touch sensing displays andfingerprint sensing functions, a fingerprint sensor tends to be aseparate device from the display screen, either placed on the samesurface of the display screen at a location outside the display screenarea such as in some models of Apple iPhones and Samsung smartphones, orplaced on the backside of a smartphone, such as some models of smartphones by Huawei, Lenovo, Xiaomi or Google, to avoid taking up valuablespace for placing a large display screen on the front side. Thosefingerprint sensors are separate devices from the display screens andthus need to be compact to save space for display and other functionswhile still providing reliable and fast fingerprint sensing with aspatial image resolution above a certain acceptable level. However, theneed to be compact and small and the need to provide a high spatialimage resolution in capturing a fingerprint pattern are in directconflict with each other in many fingerprint sensors because a highspatial image resolution in capturing a fingerprint pattern in based onvarious suitable fingerprint sensing technologies (e.g., capacitivetouch sensing or optical imaging) requires a large sensor area with alarge number of sensing pixels.

The sensor technology and examples of implementations of the sensortechnology described in this patent document provide an optical sensormodule that uses, at least in part, the light from a display screen asthe illumination probe light to illuminate a fingerprint sensing area onthe touch sensing surface of the display screen to perform one or moresensing operations based on optical sensing of such light. A suitabledisplay screen for implementing the disclosed optical sensor technologycan be based on various display technologies or configurations,including, a display screen having light emitting display pixels withoutusing backlight where each individual pixel generates light for forminga display image on the screen such as liquid crystal display (LCD)screens an organic light emitting diode (OLED) display screens, orelectroluminescent display screens.

In the disclosed examples for integrating optical sensing to LCD basedon the disclosed optical sensor technology, the under LCD optical sensorcan be used to detect a portion of the light that is used for displayingimages in a LCD screen where such a portion of the light for the displayscreen may be the scattered light, reflected light or some stray light.For example, in some implementations, the image light of the LCD screenbased on backlighting may be reflected or scattered back into the LCDdisplay screen as returned light when encountering an object such as auser finger or palm, or a user pointer device like a stylus. Suchreturned light can be captured for performing one or more opticalsensing operations using the disclosed optical sensor technology. Due tothe use of the light from LCD screen for optical sensing, an opticalsensor module based on the disclosed optical sensor technology isspecially designed to be integrated to the LCD display screen in a waythat maintains the display operations and functions of the LCD displayscreen without interference while providing optical sensing operationsand functions to enhance overall functionality, device integration anduser experience of an electronic device or system such as a smart phone,a tablet, or a mobile/wearable device.

In addition, in various implementations of the disclosed optical sensingtechnology, one or more designated probe light sources may be providedto produce additional illumination probe light for the optical sensingoperations by the under LCD screen optical sensing module. In suchapplications, the light from the backlighting of the LCD screen and theprobe light from the one or more designated probe light sourcescollectively form the illumination light for optical sensing operations.

Regarding the additional optical sensing functions beyond fingerprintdetection, the optical sensing may be used to measure other parameters.For example, the disclosed optical sensor technology can measure apattern of a palm of a person given the large touch area available overthe entire LCD display screen (in contrast, some designated fingerprintsensors such as the fingerprint senor in the home button of Apple'siPhone/iPad devices have a rather small and designated off-screenfingerprint sensing area that is highly limited in the sensing area sizethat may not be suitable for sensing large patterns). For yet anotherexample, the disclosed optical sensor technology can be used not only touse optical sensing to capture and detect a pattern of a finger or palmthat is associated with a person, but also to use optical sensing orother sensing mechanisms to detect whether the captured or detectedpattern of a fingerprint or palm is from a live person's hand by a “livefinger” detection mechanism, which may be based on, for example, thedifferent optical absorption behaviors of the blood at different opticalwavelengths, the fact that a live person's finger tends to be moving orstretching due to the person's natural movement or motion (eitherintended or unintended) or pulsing when the blood flows through theperson's body in connection with the heartbeat. In one implementation,the optical sensor module can detect a change in the returned light froma finger or palm due to the heartbeat/blood flow change and thus todetect whether there is a live heartbeat in the object presented as afinger or palm. The user authentication can be based on the combinationof the both the optical sensing of the fingerprint/palm pattern and thepositive determination of the presence of a live person to enhance theaccess control. For yet another example, the optical sensor module mayinclude a sensing function for measuring a glucose level or a degree ofoxygen saturation based on optical sensing in the returned light from afinger or palm. As yet another example, as a person touches the LCDdisplay screen, a change in the touching force can be reflected in oneor more ways, including fingerprint pattern deforming, a change in thecontacting area between the finger and the screen surface, fingerprintridge widening, or a blood flow dynamics change. Those and other changescan be measured by optical sensing based on the disclosed optical sensortechnology and can be used to calculate the touch force. This touchforce sensing can be used to add more functions to the optical sensormodule beyond the fingerprint sensing.

With respect to useful operations or control features in connection withthe touch sensing aspect of the LCD display screen, the disclosedoptical sensor technology can provide triggering functions or additionalfunctions based on one or more sensing results from the optical sensormodule to perform certain operations in connection with the touchsensing control over the LCD display screen. For example, the opticalproperty of a finger skin (e.g., the index of refraction) tends to bedifferent from other artificial objects. Based on this, the opticalsensor module may be designed to selectively receive and detect returnedlight that is caused by a finger in touch with the surface of the LCDdisplay screen while returned light caused by other objects would not bedetected by the optical sensor module. This object-selective opticaldetection can be used to provide useful user controls by touch sensing,such as waking up the smartphone or device only by a touch via aperson's finger or palm while touches by other objects would not causethe device to wake up for energy efficient operations and to prolong thebattery use. This operation can be implemented by a control based on theoutput of the optical sensor module to control the waking up circuitryoperation of the LCD display screen which, the LCD pixels are put in a“sleep” mode by being turned off (and the LCD backlighting is alsoturned off) while one or more illumination light sources (e.g., LEDs)for the under-LCD panel optical sensor module are turned on in a flashmode to intermittently emit flash light to the screen surface forsensing any touch by a person's finger or palm. Under this design, theoptical sensor module operates the one or more illumination lightsources to produce the “sleep” mode wake-up sensing light flashes sothat the optical sensor module can detect returned light of such wake-upsensing light caused by the finger touch on the LCD display screen and,upon a positive detection, the LCD backlighting and the LCD displayscreen are turned on or “woken up”. In some implementations, the wake-upsensing light can be in the infrared invisible spectral range so a userwill not experience any visual of a flash light. The LCD display screenoperation can be controlled to provide an improved fingerprint sensingby eliminating background light for optical sensing of the fingerprint.In one implementation, for example, each display scan frame generates aframe of fingerprint signals. If, two frames of fingerprint signals withthe display are generated in one frame when the LCD display screen isturned on and in the other frame when the LCD display screen is turnedoff, the subtraction between those two frames of signals can be used toreduce the ambient background light influence. By operating thefingerprint sensing frame rate is at one half of the display frame ratein some implementations, the background light noise in fingerprintsensing can be reduced.

An optical sensor module based on the disclosed optical sensortechnology can be coupled to the backside of the LCD display screenwithout requiring creation of a designated area on the surface side ofthe LCD display screen that would occupy a valuable device surface realestate in some electronic devices such as a smartphone, a tablet or awearable device. This aspect of the disclosed technology can be used toprovide certain advantages or benefits in both device designs andproduct integration or manufacturing.

In some implementations, an optical sensor module based on the disclosedoptical sensor technology can be configured as a non-invasive modulethat can be easily integrated to a display screen without requiringchanging the design of the LCD display screen for providing a desiredoptical sensing function such as fingerprint sensing. In this regard, anoptical sensor module based on the disclosed optical sensor technologycan be independent from the design of a particular LCD display screendesign due to the nature of the optical sensor module: the opticalsensing of such an optical sensor module is by detecting the light thatis emitted by the one or more illumination light sources of the opticalsensor module and is returned from the top surface of the display area,and the disclosed optical sensor module is coupled to the backside ofthe LCD display screen as a under-screen optical sensor module forreceiving the returned light from the top surface of the display areaand thus does not require a special sensing port or sensing area that isseparate from the display screen area. Accordingly, such a under-screenoptical sensor module can be used to combine with a LCD display screento provide optical fingerprint sensing and other sensor functions on anLCD display screen without using a specially designed LCD display screenwith hardware especially designed for providing such optical sensing.This aspect of the disclosed optical sensor technology enables a widerange of LCD display screens in smartphones, tablets or other electronicdevices with enhanced functions from the optical sensing of thedisclosed optical sensor technology.

For example, for an existing phone assembly design that does not providea separate fingerprint sensor as in certain Apple iPhones or SamsungGalaxy smartphones, such an existing phone assembly design can integratethe under-screen optical sensor module as disclosed herein withoutchanging the touch sensing-display screen assembly to provide an addedon-screen fingerprint sensing function. Because the disclosed opticalsensing does not require a separate designated sensing area or port asin the case of certain Apple iPhones/Samsung Galaxy phones with a frontfingerprint senor outside the display screen area, or some smartphoneswith a designated rear fingerprint sensor on the backside like in somemodels by Huawei, Xiaomi, Google or Lenovo, the integration of theon-screen fingerprint sensing disclosed herein does not require asubstantial change to the existing phone assembly design or the touchsensing display module that has both the touch sensing layers and thedisplay layers. Based on the disclosed optical sensing technology inthis document, no external sensing port and no extern hardware buttonare needed on the exterior of a device are needed for adding thedisclosed optical sensor module for fingerprint sensing. The addedoptical sensor module and the related circuitry are under the displayscreen inside the phone housing and the fingerprint sensing can beconveniently performed on the same touch sensing surface for the touchscreen.

For another example, due to the above described nature of the opticalsensor module for fingerprint sensing, a smartphone that integrates suchan optical sensor module can be updated with improved designs, functionsand integration mechanism without affecting or burdening the design ormanufacturing of the LCD display screens to provide desired flexibilityto device manufacturing and improvements/upgrades in product cycleswhile maintaining the availability of newer versions of optical sensingfunctions to smartphones, tablets or other electronic devices using LCDdisplay screens. Specifically, the touch sensing layers or the LCDdisplay layers may be updated in the next product release without addingany significant hardware change for the fingerprint sensing featureusing the disclosed under-screen optical sensor module. Also, improvedon-screen optical sensing for fingerprint sensing or other opticalsensing functions by such an optical sensor module can be added to a newproduct release by using a new version of the under-screen opticalsensor module without requiring significant changes to the phoneassembly designs, including adding additional optical sensing functions.

The above and other features of the disclosed optical sensor technologycan be implemented to provide a new generation of electronic deviceswith improved fingerprint sensing and other sensing functions,especially for smartphones, tablets and other electronic devices withLCD display screens to provide various touch sensing operations andfunctions and to enhance the user experience in such devices. Thefeatures for optical sensor modules disclosed in this patent documentmay be applicable to various display panels based on differenttechnologies including both LCD and OLED displays The specific examplesbelow are directed to LCD display panels and optical sensor modulesplaced under LCD display panels.

In implementations of the disclosed technical features, additionalsensing functions or sensing modules, such as a biomedical sensor, e.g.,a heartbeat sensor in wearable devices like wrist band devices orwatches, may be provided. In general, different sensors can be providedin electronic devices or systems to achieve different sensing operationsand functions.

The disclosed technology can be implemented to provide devices, systems,and techniques that perform optical sensing of human fingerprints andauthentication for authenticating an access attempt to a lockedcomputer-controlled device such as a mobile device or acomputer-controlled system, that is equipped with a fingerprintdetection module. The disclosed technology can be used for securingaccess to various electronic devices and systems, including portable ormobile computing devices such as laptops, tablets, smartphones, andgaming devices, and other electronic devices or systems such aselectronic databases, automobiles, bank ATMs, etc.

FIG. 1 is a block diagram of an example of a system 180 with afingerprint sensing module 180 including a fingerprint sensor 181 whichcan be implemented to include an optical fingerprint sensor based on theoptical sensing of fingerprints as disclosed in this document. Thesystem 180 includes a fingerprint sensor control circuit 184, and adigital processor 186 which may include one or more processors forprocessing fingerprint patterns and determining whether an inputfingerprint pattern is one for an authorized user. The fingerprintsensing system 180 uses the fingerprint sensor 181 to obtain afingerprint and compares the obtained fingerprint to a storedfingerprint to enable or disable functionality in a device or system 188that is secured by the fingerprint sensing system 180. In operation, theaccess to the device 188 is controlled by the fingerprint processingprocessor 186 based on whether the captured user fingerprint is from anauthorized user. As illustrated, the fingerprint sensor 181 may includemultiple fingerprint sensing pixels such as pixels 182A-182E thatcollectively represent at least a portion of a fingerprint. For example,the fingerprint sensing system 180 may be implemented at an ATM as thesystem 188 to determine the fingerprint of a customer requesting toaccess funds or other transactions. Based on a comparison of thecustomer's fingerprint obtained from the fingerprint sensor 181 to oneor more stored fingerprints, the fingerprint sensing system 180 may,upon a positive identification, cause the ATM system 188 to grant therequested access to the user account, or, upon a negativeidentification, may deny the access. For another example, the device orsystem 188 may be a smartphone or a portable device and the fingerprintsensing system 180 is a module integrated to the device 188. For anotherexample, the device or system 188 may be a gate or secured entrance to afacility or home that uses the fingerprint sensor 181 to grant or denyentrance. For yet another example, the device or system 188 may be anautomobile or other vehicle that uses the fingerprint sensor 181 to linkto the start of the engine and to identify whether a person isauthorized to operate the automobile or vehicle.

As a specific example, FIGS. 2A and 2B illustrate one exemplaryimplementation of an electronic device 200 having a touch sensingdisplay screen assembly and an optical sensor module positionedunderneath the touch sensing display screen assembly. In this particularexample, the display technology can be implemented by a LCD displayscreen with backlight for optically illuminating the LCD pixels oranother display screen having light emitting display pixels withoutusing backlight (e.g., an OLED display screen). The electronic device200 can be a portable device such as a smartphone or a tablet and can bethe device 188 as shown in FIG. 1.

FIG. 2A shows the front side of the device 200 which may resemble somefeatures in some existing smartphones or tablets. The device screen ison the front side of the device 200 occupying either entirety, amajority or a significant portion of the front side space and thefingerprint sensing function is provided on the device screen, e.g., oneor more sensing areas for receiving a finger on the device screen. As anexample, FIG. 2A shows a fingerprint sensing zone in the device screenfor a finger to touch which may be illuminated as a visibly identifiablezone or area for a user to place a finger for fingerprint sensing. Sucha fingerprint sensing zone can function like the rest of the devicescreen for displaying images. As illustrated, the device housing of thedevice 200 may have, in various implementations, side facets thatsupport side control buttons that are common in various smartphones onthe market today. Also, one or more optional sensors may be provided onthe front side of the device 200 outside the device screen asillustrated by one example on the left upper corner of the devicehousing in FIG. 2A.

FIG. 2B shows an example of the structural construction of the modulesin the device 200 relevant to the optical fingerprint sensing disclosedin this document. The device screen assembly shown in FIG. 2B includes,e.g., the touch sensing screen module with touch sensing layers on thetop, and a display screen module with display layers located underneaththe touch sensing screen module. An optical sensor module is coupled to,and located underneath, the display screen assembly module to receiveand capture the returned light from the top surface of the touch sensingscreen module and to guide and image the returned light onto an opticalsensor array of optical sensing pixels or photodetectors which convertthe optical image in the returned light into pixel signals for furtherprocessing. Underneath the optical sensor module is the deviceelectronics structure containing certain electronic circuits for theoptical sensor module and other parts in the device 200. The deviceelectronics may be arranged inside the device housing and may include apart that is under the optical sensor module as shown in FIG. 2B.

In implementations, the top surface of the device screen assembly can bea surface of an optically transparent layer serving as a user touchsensing surface to provide multiple functions, such as (1) a displayoutput surface through which the light carrying the display imagespasses through to reach a viewer's eyes, (2) a touch sensing interfaceto receive a user's touches for the touch sensing operations by thetouch sensing screen module, and (3) an optical interface for on-screenfingerprint sensing (and possibly one or more other optical sensingfunctions). This optically transparent layer can be a rigid layer suchas a glass or crystal layer or a flexible layer.

One example of a display screen is an LCD display having LCD layers anda thin film transistor (TFT) structure or substrate. A LCD display panelis a multi-layer liquid crystal display (LCD) module that includes LCDdisplay backlighting light sources (e.g., LED lights) emitting LCDillumination light for LCD pixels, a light waveguide layer to guide thebacklighting light, and LCD structure layers which can include, e.g., alayer of liquid crystal (LC) cells, LCD electrodes, transparentconductive ITO layer, an optical polarizer layer, a color filter layer,and a touch sensing layer. The LCD module also includes a backlightingdiffuser underneath the LCD structure layers and above the lightwaveguide layer to spatially spread the backlighting light forilluminating the LCD display pixels, and an optical reflector film layerunderneath the light waveguide layer to recycle backlighting lighttowards the LCD structure layers for improved light use efficiency andthe display brightness.

Referring to FIG. 2B, the optical sensor module in this example isplaced under the LCD display panel to capture the returned light fromthe top touch sensing surface and to acquire high resolution images offingerprint patterns when user's finger is in touch with a sensing areaon the top surface. In other implementations, the disclosed under-screenoptical sensor module for fingerprint sensing may be implemented on adevice without the touch sensing feature. In addition, a suitabledisplay panel may be in various screen designs different from OLEDdisplays.

FIGS. 3A and 3B illustrate an example of a device that implements theoptical sensor module in FIGS. 2A and 2B. FIG. 3A shows a crosssectional view of a portion of the device containing the under-screenoptical sensor module. FIG. 3B shows, on the left, a view of the frontside of the device with the touch sensing display indicating afingerprint sensing area on the lower part of the display screen, and onthe right, a perspective view of a part of the device containing theoptical sensor module that is under the device display screen assembly.FIG. 3B also shows an example of the layout of the flexible tape withcircuit elements.

In the design examples in FIGS. 2A, 2B, 3A and 3B, the opticalfingerprint sensor design is different from some other fingerprintsensor designs using a separate fingerprint sensor structure from thedisplay screen with a physical demarcation between the display screenand the fingerprint sensor (e.g., a button like structure in an openingof the top glass cover in some mobile phone designs) on the surface ofthe mobile device. In the illustrated designs here, the opticalfingerprint sensor for detecting fingerprint sensing and other opticalsignals are located under the top cover glass or layer (e.g., FIG. 3A)so that the top surface of the cover glass serves as the top surface ofthe mobile device as a contiguous and uniform glass surface across boththe display screen layers and the optical detector sensor that arevertically stacked and vertically overlap. This design for integratingoptical fingerprint sensing and the touch sensitive display screen undera common and uniform surface provides benefits, including improveddevice integration, enhanced device packaging, enhanced deviceresistance to exterior elements, failure and wear and tear, and enhanceduser experience over the ownership period of the device.

Referring back to FIGS. 2A and 2B, the illustrated under-screen opticalsensor module for on-screen fingerprint sensing may be implemented invarious configurations.

In one implementation, a device based on the above design can bestructured to include a device screen a that provides touch sensingoperations and includes a LCD display panel structure for forming adisplay image, a top transparent layer formed over the device screen asan interface for being touched by a user for the touch sensingoperations and for transmitting the light from the display structure todisplay images to a user, and an optical sensor module located below thedisplay panel structure to receive light that returns from the toptransparent layer to detect a fingerprint.

This device and other devices disclosed in this document can be furtherconfigured to include various features.

For example, a device electronic control module can be included in thedevice to grant a user's access to the device if a detected fingerprintmatches a fingerprint an authorized user. In addition, the opticalsensor module is configured to, in addition to detecting fingerprints,also detect a biometric parameter different form a fingerprint byoptical sensing to indicate whether a touch at the top transparent layerassociated with a detected fingerprint is from a live person, and thedevice electronic control module is configured to grant a user's accessto the device if both (1) a detected fingerprint matches a fingerprintan authorized user and (2) the detected biometric parameter indicatesthe detected fingerprint is from a live person. The biometric parametercan include, e.g., whether the finger contains a blood flow, or aheartbeat of a person.

For example, the device can include a device electronic control modulecoupled to the display panel structure to supply power to the lightemitting display pixels and to control image display by the displaypanel structure, and, in a fingerprint sensing operation, the deviceelectronic control module operates to turn off the light emittingdisplay pixels in one frame to and turn on the light emitting displaypixels in a next frame to allow the optical sensor array to capture twofingerprint images with and without the illumination by the lightemitting display pixels to reduce background light in fingerprintsensing.

For another example, a device electronic control module may be coupledto the display panel structure to supply power to the LCD display paneland to turn off power to the backlighting of the LCD display panel in asleep mode, and the device electronic control module may be configuredto wake up the display panel structure from the sleep mode when theoptical sensor module detects the presence of a person's skin at thedesignated fingerprint sensing region of the top transparent layer. Morespecifically, in some implementations, the device electronic controlmodule can be configured to operate one or more illumination lightsources in the optical sensor module to intermittently emit light, whileturning off power to the LCD display panel (in the sleep mode), todirect the intermittently emitted illumination light to the designatedfingerprint sensing region of the top transparent layer for monitoringwhether there is a person's skin in contact with the designatedfingerprint sensing region for waking up the device from the sleep mode.

For another example, the device can include a device electronic controlmodule coupled to the optical sensor module to receive information onmultiple detected fingerprints obtained from sensing a touch of a fingerand the device electronic control module is operated to measure a changein the multiple detected fingerprints and determines a touch force thatcauses the measured change. For instance, the change may include achange in the fingerprint image due to the touch force, a change in thetouch area due to the touch force, or a change in spacing of fingerprintridges.

For another example, the top transparent layer can include a designatedfingerprint sensing region for a user to touch with a finger forfingerprint sensing and the optical sensor module below the displaypanel structure can include a transparent block in contact with thedisplay panel substrate to receive light that is emitted from thedisplay panel structure and returned from the top transparent layer, anoptical sensor array that receives the light and an optical imagingmodule that images the received light in the transparent block onto theoptical sensor array. The optical sensor module can be positionedrelative to the designated fingerprint sensing region and structured toselectively receive returned light via total internal reflection at thetop surface of the top transparent layer when in contact with a person'sskin while not receiving the returned light from the designatedfingerprint sensing region in absence of a contact by a person's skin.

For yet another example, the optical sensor module can be structured toinclude an optical wedge located below the display panel structure tomodify a total reflection condition on a bottom surface of the displaypanel structure that interfaces with the optical wedge to permitextraction of light out of the display panel structure through thebottom surface, an optical sensor array that receives the light from theoptical wedge extracted from the display panel structure, and an opticalimaging module located between the optical wedge and the optical sensorarray to image the light from the optical wedge onto the optical sensorarray.

Specific examples of under-screen optical sensor modules for on-screenfingerprint sensing are provided below.

FIG. 4A and FIG. 4B show an example of one implementation of an opticalsensor module under the display screen assembly for implementing thedesign in FIGS. 2A and 2B. The device in FIGS. 4A-4B includes a displayassembly 423 with a top transparent layer 431 formed over the devicescreen assembly 423 as an interface for being touched by a user for thetouch sensing operations and for transmitting the light from the displaystructure to display images to a user. This top transparent layer 431can be a cover glass or a crystal material in some implementations. Thedevice screen assembly 423 can include a LCD display module 433 underthe top transparent layer 431. The LCD display layers allow partialoptical transmission so light from the top surface can partiallytransmit through the LCD display layers to reach the under-LCD opticalsensor module. For example, LCD display layers include electrodes andwiring structure optically acting as an array of holes and lightscattering objects. A device circuit module 435 may be provided underthe LCD display panel to control operations of the device and performfunctions for the user to operate the device.

The optical sensor module 702 in this particular implementation exampleis placed under LCD display module 433. One or more illumination lightsources 703 are provided for the optical sensor module 702 and can becontrolled to emit light to at least partially pass through the LCDdisplay module 433 to illuminate the fingerprint sensing zone 615 on thetop transparent layer 431 within the device screen area for a user toplace a finger therein for fingerprint identification. The illuminationlight from the one or more illumination light sources 703 can bedirected to the fingerprint sensing area 615 on the top surface as ifsuch illumination light is from a fingerprint illumination light zone613. As illustrated, a finger 445 is placed in the illuminatedfingerprint sensing zone 615 as the effective sensing zone forfingerprint sensing. A portion of the reflected or scattered light inthe zone 615 is directed into the optical sensor module underneath theLCD display module 433 and a photodetector sensing array inside theoptical sensor module receives such light and captures the fingerprintpattern information carried by the received light.

In this design of using one or more illumination light sources 703 toprovide the illumination light for optical fingerprint sensing, eachillumination light source 703 maybe controlled in some implementationsto turn on intermittently with a relatively low cycle to reduce thepower used for the optical sensing operations. The fingerprint sensingoperation can be implemented in a 2-step process in someimplementations: first, the one or more illumination light sources 703are turned on in a flashing mode without turning on the LCD displaypanel to use the flashing light to sense whether a finger touches thesensing zone 615 and, once a touch in the zone 615 is detected, theoptical sensing module is operated to perform the fingerprint sensingbased on optical sensing and the LCD display panel may be turned on.

In the example in FIG. 4B, the under-screen optical sensor moduleincludes a transparent block 701 that is coupled to the display panel toreceive the returned light from the top surface of the device assembly,and an optical imaging block 702 that performs the optical imaging andimaging capturing. Light from the illumination light source 703, afterreaching the cover top surface, e.g., the cover top surface at thesensing area 615 where a user finger touches, is reflected or scatteredback from the cover top surface. When fingerprint ridges in closecontact of the cover top surface in the sensing area 615, the lightreflection under the fingerprint ridges is different, due to thepresence of the skin or tissue of the finger in contact at thatlocation, from the light reflection at another location under thefingerprint valley, where the skin or tissue of the finger is absent.This difference in light reflection conditions at the locations of theridges and valleys in the touched finger area on the cover top surfaceforms an image representing an image or spatial distribution of theridges and valleys of the touched section of the finger. The reflectionlight is directed back towards the LCD display module 433, and, afterpassing through the small holes of the LCD display module 433, reachesthe interface with the low index optically transparent block 701 of theoptical sensor module. The low index optically transparent block 701 isconstructed to have a refractive index less than a refractive index ofthe LCD display panel so that the returned light can be extracted out ofthe LCD display panel into the optically transparent block 701. Once thereturned light is received inside the optically transparent block 701,such received light enters the optical imaging unit as part of theimaging sensing block 702 and is imaged onto the photodetector sensingarray or optical sensing array inside the block 702. The lightreflection differences between fingerprint ridges and valleys create thecontrast of the fingerprint image. As shown in FIG. 4B, a controlcircuit 704 (e.g., a microcontroller or MCU) is coupled to the imagingsensing block 702 and to other circuitry such as the device mainprocessor 705 on a main circuit board.

In this particular example, the optical light path design is such thelight ray enters the cover top surface within the total reflect angleson the top surface between the substrate and air interface will getcollected most effectively by the imaging optics and imaging sensorarray in the block 702. In this design the image of the fingerprintridge/valley area exhibits a maximum contrast. Such an imaging systemmay have undesired optical distortions that would adversely affect thefingerprint sensing. Accordingly, the acquired image may be furthercorrected by a distortion correction during the imaging reconstructionin processing the output signals of the optical sensor array in theblock 702 based on the optical distortion profile along the light pathsof the returned light at the optical sensor array. The distortioncorrection coefficients can be generated by images captured at eachphotodetector pixel by scanning a test image pattern one line pixel at atime, through the whole sensing area in both X direction lines and Ydirection lines. This correction process can also use images from tuningeach individual pixel on one at a time, and scanning through the wholeimage area of the photodetector array. This correction coefficients onlyneed to be generated one time after assembly of the sensor.

The background light from environment (e.g., sun light or room light)may enter the image sensor through the LCD panel top surface, throughholes in the LCDD display assembly 433. Such background light can createa background baseline in the interested images from fingers and isundesirable. Different methods can be used to reduce this baselineintensity. One example is to tune on and off the illumination lightsource 703 at a certain frequency f and the image sensor accordinglyacquires the received images at the same frequency by phasesynchronizing the light source driving pulse and image sensor frame.Under this operation, only one of the image phases contain light fromthe light source. By subtracting even and odd frames, it is possible toobtain an image which most consists of light emitted from the modulatedillumination light source. Based on this design, each display scan framegenerates a frame of fingerprint signals. If two sequential frames ofsignals by turning on the illumination light in one frame and off in theother frame are subtracted, the ambient background light influence canbe minimized or substantially eliminated. In implementations, thefingerprint sensing frame rate can be one half of the display framerate.

A portion of the light from the illumination light source 703 may alsogo through the cover top surface and enter the finger tissues. This partof light power is scattered around and a part of this scattered lightmay be eventually collected by the imaging sensor array in the opticalsensor module. The light intensity of this scattered light depends onthe finger's skin color, the blood concentration in the finger tissueand this information carried by this scattered light on the finger isuseful for fingerprint sensing and can be detected as part of thefingerprint sensing operation. For example, by integrating the intensityof a region of user's finger image, it is possible to observe the bloodconcentration increase/decrease depends on the phase of the user'sheart-beat. This signature can be used to determine the user's heartbeat rate, to determine if the user's finger is a live finger, or toprovide a spoof device with a fabricated fingerprint pattern.

The one or more illumination light sources 703 in FIG. 4B can bedesigned to emit light of different colors or wavelengths and theoptical sensor module can capture returned light from a person's fingerat the different colors or wavelengths. By recording the correspondingmeasured intensity of the returned light at the different colors orwavelengths, information associated with the user's skin color can bedetermined. As an example, when a user registers a finger forfingerprint authentication operation, the optical fingerprint sensoralso measures intensity of the scatter light from finger at color A, andB, as intensity Ia, Ib. The ratio of Ia/Ib could be recorded to comparewith later measurement when user's finger is placed on the sensing areato measure fingerprint. This method can help reject the spoof devicewhich may not match user's skin color.

The one or more illumination light sources 703 can be controlled by thesame electronics 704 (e.g., MCU) for controlling the image sensor arrayin the block 702. The one or more illumination light sources 703 can bepulsed for a short time, at a low duty cycle, to emit lightintermittently and to provide pulse light for image sensing. The imagesensor array can be operated to monitor the light pattern at the samepulse duty cycle. If there is a human finger touching the sensing area615 on the screen, the image that is captured at the imaging sensingarray in the block 702 can be used to detect the touching event. Thecontrol electronics or MCU 704 connected to the image sensor array inthe block 702 can be operated to determine if the touch is by a humanfinger touch. If it is confirmed that it is a human finger touch event,the MCU 704 can be operated to wake up the smartphone system, turn onthe illumination light source 703 for performing the optical fingerprintsensing), and use the normal mode to acquire a full fingerprint image.The image sensor array in the block 702 will send the acquiredfingerprint image to the smartphone main processor 705 which can beoperated to match the captured fingerprint image to the registeredfingerprint database. If there is a match, the smartphone will unlockthe phone, and start the normal operation. If the captured image is notmatched, the smartphone will feedback to user that the authentication isfailed. User may try again, or input passcode.

In the example in FIGS. 4A and 4B, the under-screen optical sensormodule uses the optically transparent block 701 and the imaging sensingblock 702 with the photodetector sensing array to optically image thefingerprint pattern of a touching finger in contact with the top surfaceof the display screen onto the photodetector sensing array. The opticalimaging axis or detection axis 625 from the sensing zone 615 to thephotodetector array in the block 702 is illustrated in FIG. 4B. Theoptically transparent block 701 and the front end of the imaging sensingblock 702 before the photodetector sensing array forma a bulk imagingmodule to achieve proper imaging for the optical fingerprint sensing.Due to the optical distortions in this imaging process, a distortioncorrection can be used, as explained above, to achieve the desiredimaging operation.

In the optical sensing by the under-screen optical sensor module inFIGS. 4A and 4B and other designs disclosed herein, the optical signalfrom the sensing zone 615 on the top transparent layer 431 to theunder-screen optical sensor module include different light components.FIGS. 5A, 5B and 5C illustrate signal generation for the returned lightfrom the sensing zone 615 under different optical conditions tofacilitate the understanding of the operation of the under-screenoptical sensor module.

FIG. 5A shows an example of how illumination light from the illuminationlight source 703 propagates through the OLED display module 433, aftertransmitting through the top transparent layer 431, and generatesdifferent returned light signals including light signals that carryfingerprint pattern information to the under-screen optical sensormodule. For simplicity, two illumination rays 80 and 82 at two differentlocations are directed to the top transparent layer 431 withoutexperiencing total reflection at the interfaces of the top transparentlayer 431. Specifically, the illumination light rays 80 and 82 areperpendicular or nearly perpendicular to the top layer 431. A finger 60is in contact with the sensing zone 615 on the e top transparent layer431. As illustrated, the illumination light beam 80 reaches to a fingerridge in contact with the top transparent layer 431 after transmittingthrough the top transparent layer 431 to generate the light beam 183 inthe finger tissue and another light beam 181 back towards the LCDdisplay module 433. The illumination light beam 82 reaches to a fingervalley located above the top transparent layer 431 after transmittingthrough the top transparent layer 431 to generate the reflected lightbeam 185 from the interface with the top transparent layer 431 backtowards the LCD display module 433, a second light beam 189 that entersthe finger tissue and a third light beam 187 reflected by the fingervalley.

In the example in FIG. 5A, it is assumed that the finger skin'sequivalent index of refraction is about 1.44 at 550 nm and the coverglass index of refraction is about 1.51 for the top transparent layer431. The finger ridge-cover glass interface reflects part of the beam 80as reflected light 181 to bottom layers 524 below the LCD display module433. The reflectance can be low, e.g., about 0.1% in some LCD panels.The majority of the light beam 80 becomes the beam 183 that transmitsinto the finger tissue 60 which causes scattering of the light 183 toproduce the returned scattered light 191 towards the LCD display module433 and the bottom layers 524. The scattering of the transmitted lightbeam 189 from the LCD pixel 73 in the finger tissue also contributes tothe returned scattered light 191.

The beam 82 at the finger skin valley location 63 is reflected by thecover glass surface (e.g., about 3.5% as the reflected light 185 towardsbottom layers 524, and the finger valley surface reflects about 3.3% ofthe incident light power (light 187) to bottom layers 524. The totalreflection may be about 6.8%. The majority light 189 is transmitted intothe finger tissues 60. Part of the light power in the transmitted light189 in the figure tissue is scattered by the tissue to contribute to thescattered light 191 towards and into the bottom layers 524.

Therefore, the light reflections from various interface or surfaces atfinger valleys and finger ridges of a touching finger are different andthe reflection ratio difference carries the fingerprint map informationand can be measured to extract the fingerprint pattern of the portionthat is in contact with the top transparent layer 431 and is illuminatedthe OLED light.

FIGS. 5B and 5C illustrate optical paths of two additional types ofillumination light rays at the top surface under different conditionsand at different positions relative to valleys or ridges of a finger,including under a total reflection condition at the interface with thetop transparent layer 431. The illustrated illumination light raysgenerate different returned light signals including light signals thatcarry fingerprint pattern information to the under-screen optical sensormodule. It is assumed that the cover glass 431 and the LCD displaymodule 433 are glued together without any air gap in between so thatillumination light with a large incident angle to the cover glass 431will be totally reflected at the cover glass-air interface. FIG. 5A, 5Band 5C illustrate examples of three different groups divergent lightbeams: (1) central beams 82 with small incident angles to the coverglass 431 without the total reflection (FIG. 5A), (2) high contrastbeams 201, 202, 211, 212 that are totally reflected at the cover glass431 when nothing touches the cover glass surface and can be coupled intofinger tissues when a finger touches the cover glass 431 (FIGS. 5B and5C), and (3) escaping beams having very large incident angles that aretotally reflected at the cover glass 431 even at a location where thefinger issue is in contact.

For the central light beams 82, the cover glass surface reflects about0.1%˜3.5% to light beam 185 that is transmitted into bottom layers 524,the finger skin reflects about 0.1%˜3.3% to light beam 187 that is alsotransmitted into bottom layers 524. The reflection difference isdependent on whether the light beams 82 meet with finger skin ridge 61or valley 63. The rest light beam 189 is coupled into the finger tissues60.

For high contrast light beams 201 and 202, the cover glass surfacereflects nearly 100% to light beams 205 and 206 respectively if nothingtouches the cover glass surface. When the finger skin ridges touch thecover glass surface and at light beams 201 and 202 positions, most ofthe light power is coupled into the finger tissues 60 by light beams 203and 204.

For high contrast light beams 211 and 212, the cover glass surfacereflects nearly 100% to light beams 213 and 214 respectively if nothingtouches the cover glass surface. When the finger touches the cover glasssurface and the finger skin valleys happen to be at light beams 211 and212 positions, no light power is coupled into finger tissues 60.

As illustrated in FIG. 5A, light beams that are coupled into fingertissues 60 will experience random scattering by the figure tissues toform low-contrast light 191 and part of such low-contrast light 191 willpass through the LCD display module 433 to reach to the optical sensormodule.

Therefore, in high contrast light beams illuminated area, finger skinridges and valleys cause different optical reflections and thereflection difference pattern carries the fingerprint patterninformation. The high contrast fingerprint signals can be achieved bycomparing the difference.

The disclosed under-screen optical sensing technology can be in variousconfigurations to optically capture fingerprints based on the design inFIGS. 2A and 2B.

For example, the specific implementation in FIG. 4B based on opticalimaging by using a bulk imaging module in the optical sensing module canbe implemented in various configurations. FIGS. 6A-6C, 7, 8A-8B, 9,10A-10B, 11 and 12 illustrate examples of various implementations andadditional features and operations of the under-screen optical sensormodule designs for optical fingerprint sensing.

FIG. 6A, FIG. 6B and FIG. 6C show an example of a under-screen opticalsensor module based on optical imaging via a lens for capturing afingerprint from a finger 445 pressing on the display cover glass 423.FIG. 6C is an enlarged view of the optical sensor module part shown inFIG. 6B. The under-screen optical sensor module as shown in FIG. 6B isplaced under the LCD display module 433 includes an opticallytransparent spacer 617 that is engaged to the bottom surface of the LCDdisplay module 433 to receive the returned light from the sensing zone615 on the top surface of the top transparent layer 431, an imaging lens621 that is located between and spacer 617 and the photodetector array623 to image the received returned light from the sensing zone 615 ontothe photodetector array 623. Like the imaging system in the example inFIG. 4B, this imaging system in FIG. 6B for the optical sensor modulecan experience image distortions and a suitable optical correctioncalibration can be used to reduce such distortions, e.g., the distortioncorrection methods described for the system in FIG. 4B.

Similar to the assumptions in FIGS. 5A, 5B and 5C, it is assumed thatthe finger skin's equivalent index of refraction to be about 1.44 at 550nm and a bare cover glass index of refraction to be about 1.51 for thecover glass 423. When the OLED display module 433 is glued onto thecover glass 431 without any air gap, the total inner reflection happensin large angles at or larger than the critical incident angle for theinterface. The total reflection incident angle is about 41.8° if nothingis in contact with the cover glass top surface, and the total reflectionangle is about 73.7° if the finger skin touches the cover glass topsurface. The corresponding total reflection angle difference is about31.9°.

In this design, the micro lens 621 and the photodiode array 623 define aviewing angle θ for capturing the image of the a contact finger in thesensing zone 615. This viewing angle can be aligned properly bycontrolling the physical parameters or configurations in order to detecta desired part of the cover glass surface in the sensing zone 615. Forexample, the viewing angle may be aligned to detect the total innerreflection of the LCD display assembly. Specifically, the viewing angleθ is aligned to sense the effective sensing zone 615 on the cover glasssurface. The effective sensing cover glass surface 615 may be viewed asa mirror so that the photodetector array effectively detects an image ofthe fingerprint illumination light zone 613 in the LCD display that isprojected by the sensing cover glass surface 615 onto the photodetectorarray. The photodiode/photodetector array 623 can receive the image ofthe zone 613 that is reflected by the sensing cover glass surface 615.When a finger touches the sensing zone 615, some of the light can becoupled into the fingerprint's ridges and this will cause thephotodetector array to receive light from the location of the ridges toappear as a darker image of the fingerprint. Because the geometrics ofthe optical detection path are known, the fingerprint image distortioncaused in the optical path in the optical sensor module can becorrected.

Consider, as a specific example, that the distance H in FIG. 6B from thedetection module central axis to the cover glass top surface is 2 mm.This design can directly cover 5 mm of an effective sensing zone 615with a width Wc on the cover glass. Adjusting the spacer 617 thicknesscan adjust the detector position parameter H, and the effective sensingzone width Wc can be optimized. Because H includes the thickness of thecover glass 431 and the display module 433, the application designshould take these layers into account. The spacer 617, the micro lens621, and the photodiode array 623 can be integrated under the colorcoating 619 on the bottom surface of the top transparent layer 431.

FIG. 7 shows an example of further design considerations of the opticalimaging design for the optical sensor module shown in FIGS. 6A-6C byusing a special spacer 618 to replace the spacer 617 in FIGS. 6B-6C toincrease the size of the sensing area 615. The spacer 618 is designedwith a width Ws and thickness is Hs to have a low refraction index (RI)ns, and is placed under the LCD display module 433, e.g., being attached(e.g., glued) to the bottom surface the LCD display module 433. The endfacet of the spacer 618 is an angled or slanted facet that interfaceswith the micro lens 621. This relative position of the spacer and thelens is different from FIGS. 6B-6C where the lens is placed underneaththe spacer 617. The micro lens 621 and a photodiode array 623 areassembled into the optical detection module with a detection angle widthθ. The detection axis 625 is bent due to optical refraction at theinterface between the spacer 618 and display module 433 and at theinterface between the cover glass 431 and the air. The local incidentangle ϕ1 and ϕ2 are decided by the refractive indices RIs, ns, nc, andna of the materials for the components.

If nc is greater than ns, ϕ1 is greater than ϕ2. Thus, the refractionenlarges the sensing width Wc. For example, assuming the finger skin'sequivalent RI is about 1.44 at 550 nm and the cover glass index RI isabout 1.51, the total reflection incident angle is estimated to be about41.8° if nothing touches the cover glass top surface, and the totalreflection angle is about 73.7° if the finger skin touches the coverglass top surface. The corresponding total reflection angle differenceis about 31.9°. If the spacer 618 is made of same material of the coverglass, and the distance from the detection module center to the coverglass top surface is 2 mm, if detection angle width is θ=31.9°, theeffective sensing area width Wc is about 5 mm. The corresponding centralaxis's local incident angle is ϕ1=ϕ2=57.75°. If the material for thespecial spacer 618 has a refractive index ns about 1.4, and Hs is 1.2 mmand the detection module is tilted at ϕ1=70°. The effective sensing areawidth is increased to be greater than 6.5 mm. Under those parameters,the detection angle width in the cover glass is reduced to 19°.Therefore, the imaging system for the optical sensor module can bedesigned to desirably enlarge the size of the sensing area 615 on thetop transparent layer 431.

When the RI of the special spacer 618 is designed to be sufficiently low(e.g., to use MgF2, CaF2, or even air to form the spacer), the width Wcof the effective sensing area 615 is no longer limited by the thicknessof the cover glass 431 and the display module 433. This propertyprovides desired design flexibility. In principle, if the detectionmodule has a sufficient resolution, the effective sensing area may evenbe increased to cover the entire display screen.

Since the disclosed optical sensor technology can be used to provide alarge sensing area for capturing a pattern, the disclosed under-screenoptical sensor modules may be used to capture and detect not only apattern of a finger but a larger size patter such a person's palm thatis associated with a person for user authentication.

FIGS. 8A-8B show an example of further design considerations of theoptical imaging design for the optical sensor module shown in FIG. 7 bysetting the detection angle θ′ of the photodetector array relative inthe display screen surface and the distance L between the lens 621 andthe spacer 618. FIG. 8A shows a cross-sectional view along the directionperpendicular to the display screen surface and FIG. 8B shows a view ofthe device from either the bottom or top of the displace screen. Afilling material 618 c can be used to fill the space between the lens621 and the photodetector array 623. For example, the filling material618 c can be same material of the special spacer 618 or anotherdifferent material. In some designs, the filling material 618 c may theair space.

FIG. 9 shows another example of a under-screen optical sensor modulebased on the design in FIG. 7 where one or more illumination lightsources 61 are provided to illuminate the top surface sensing zone 615for optical fingerprint sensing. The illumination light sources 614 maybe of an expanded type, or be a collimated type so that all the pointswithin the effective sensing zone 615 is illuminated. The illuminationlight sources 614 may be a single element light source or an array oflight sources.

FIGS. 10A-10B show an example of a under-screen optical sensor modulethat uses an optical coupler 628 shaped as a thin wedge to improve theoptical detection at the optical sensor array 623. FIG. 10A shows across section of the device structure with an under-screen opticalsensor module for fingerprint sensing and FIG. 10B shows a top view ofthe device screen. The optical wedge 628 (with a refractive index n_(s))is located below the display panel structure to modify a totalreflection condition on a bottom surface of the display panel structurethat interfaces with the optical wedge 628 to permit extraction of lightout of the display panel structure through the bottom surface. Theoptical sensor array 623 receives the light from the optical wedge 628extracted from the display panel structure and the optical imagingmodule 621 is located between the optical wedge 628 and the opticalsensor array 623 to image the light from the optical wedge 628 onto theoptical sensor array 623. In the illustrated example, the optical wedge628 includes a slanted optical wedge surface facing the optical imagingmodule and the optical sensing array 623. Also, as shown, there is afree space between the optical wedge 628 and the optical imaging module621.

If the light is totally reflected at the sensing surface of the coverglass 431, the reflectance is 100%, of the highest efficiency. However,the light will also be totally reflected at the LCD bottom surface 433 bif it is parallel to the cover glass surfaces. The wedge coupler 628 isused to modify the local surface angle so that the light can be coupledout for the detection at the optical sensor array 623. The micro holesin the LCD display module 433 provide the desired light propagation pathfor light to transmit through the LCD display module 433 for theunder-screen optical sensing. The actual light transmission efficiencymay gradually be reduced if the light transmission angle becomes toolarge or when the TFT layer becomes too thick. When the angle is closeto the total reflection angle, namely about 41.8° when the cover glassrefractive index is 1.5, the fingerprint image looks good. Accordingly,the wedge angle of the wedge coupler 628 may be adjusted to be of acouple of degrees so that the detection efficiency can be increased oroptimized. If the cover glass' refractive index is selected to behigher, the total reflection angle becomes smaller. For example, if thecover glass is made of Sapphire which refractive index is about 1.76,the total reflection angle is about 34.62°. The detection lighttransmission efficiency in the display is also improved. Therefore, thisdesign of using a thin wedge to set the detection angle to be higherthan the total reflection angle, and/or to use high refractive indexcover glass material to improve the detection efficiency.

In the under-screen optical sensor module designs in FIGS. 6A-10B, thesensing area 615 on the top transparent surface is not vertical orperpendicular to the detection axis 625 of the optical sensor module sothat the image plane of the sensing area is also not vertical orperpendicular to the detection axis 625. Accordingly, the plane of thephotodetector array 523 can be tilted relative the detection axis 625 toachieve high quality imaging at the photodetector array 623.

FIG. 11 shows three example configurations for this tiling. FIG. 11 (1)shows the sensing area 615 a is tilted and is not perpendicular thedetection axis 625. In a specified case shown in (2), the sensing area615 b is aligned to be on the detection axis 625, its image plane willalso be located on the detection axis 625. In practice, the lens 621 canbe partially cut off so as to simplify the package. In variousimplementations, the micro lens 621 can also be of transmission type orreflection type. For example, a specified approach is illustrated in(3). The sensing area 615 c is imaged by an imaging mirror 621 a. Aphotodiode array 623 b is aligned to detect the signals.

In the above designs where the lens 621 is used, the lens 621 can bedesigned to have an effective aperture that is larger than the apertureof the holes in the LCD display layers that allow transmission of lightthrough the LCD display module for optical fingerprint sensing. Thisdesign can reduce the undesired influence of the wiring structures andother scattering objects in the LCD display module.

FIG. 12 shows an example of an operation of the fingerprint sensor forreducing or eliminating undesired contributions from the backgroundlight in fingerprint sensing. The optical sensor array can be used tocapture various frames and the captured frames can be used to performdifferential and averaging operations among multiple frames to reducethe influence of the background light. For example, in frame A, theillumination light source for optical fingerprint sensing is turned onto illuminate the finger touching area, in frame B the illumination ischanged or turned off. Subtraction of the signals of frame B from thesignals of frame A can be used in the image processing to reduce theundesired background light influence.

The undesired background light in the fingerprint sensing may also bereduced by providing proper optical filtering in the light path. One ormore optical filters may be used to reject the environment lightwavelengths, such as near IR and partial of the red light etc. In someimplementation, such optical filter coatings may be made on the surfacesof the optical parts, including the display bottom surface, prismsurfaces, sensor surface etc. For example, human fingers absorb most ofthe energy of the wavelengths under ˜580 nm, if one or more opticalfilters or optical filtering coatings can be designed to reject light inwavelengths from 580 nm to infrared, undesired contributions to theoptical detection in fingerprint sensing from the environment light maybe greatly reduced.

FIG. 13 shows an example of an operation process for correcting theimage distortion in the optical sensor module. At step 1301, the one ormore illumination light sources are controlled and operated to emitlight in a specific region, and the light emission of such pixels ismodulated by a frequency F. Ate step 1302, an imaging sensor under thedisplay panel is operated to capture the image at frame rate at samefrequency F. In the optical fingerprint sensing operation, a finger isplaced on top of the display panel cover substrate and the presence ofthe finger modulates the light reflection intensity of the display panelcover substrate top surface. The imaging sensor under the displaycaptures the fingerprint modulated reflection light pattern. At step1303, the demodulation of the signals from image sensors is synchronizedwith the frequency F, and the background subtraction is performed. Theresultant image has a reduced background light effect and includesimages from pixel emitting lights. At step 1304, the capture image isprocessed and calibrated to correct image system distortions. At step1305, the corrected image is used as a human fingerprint image for userauthentication.

The same optical sensors used for capturing the fingerprint of a usercan be used also to capture the scattered light from the illuminatedfinger as shown by the back scattered light 191 in FIG. 5A. The detectorsignals from the back scattered light 191 in FIG. 5A in a region ofinterest can be integrated to produce an intensity signal. The intensityvariation of this intensity signal is evaluated to determine the heartrate of the user.

The above fingerprint sensor may be hacked by malicious individuals whocan obtain the authorized user's fingerprint, and copy the stolenfingerprint pattern on a carrier object that resembles a human finger.Such unauthorized fingerprint patterns may be used on the fingerprintsensor to unlock the targeted device. Hence, a fingerprint pattern,although a unique biometric identifier, may not be by itself acompletely reliable or secure identification. The under-screen opticalsensor module can also be used to as an optical anti-spoofing sensor forsensing whether an input object with fingerprint patterns is a fingerfrom a living person and for determining whether a fingerprint input isa fingerprint spoofing attack. This optical anti-spoofing sensingfunction can be provided without using a separate optical sensor. Theoptical anti-spoofing can provide high-speed responses withoutcompromising the overall response speed of the fingerprint sensingoperation.

FIG. 14 shows exemplary optical extinction coefficients of materialsbeing monitored in blood where the optical absorptions are differentbetween the visible spectral range e.g., red light at 660 nm and theinfrared range, e.g., IR light at 940 nm. By using probe light toilluminate a finger at a first visible wavelength (Color A) and a seconddifferent wavelength such as an IR wavelength (Color B), the differencesin the optical absorption of the input object can be captured determinewhether the touched object is a finger from a live person. The one ormore illumination light sources for providing the illumination foroptical sensing can be used to emit light of different colors to emitprobe or illumination light at least two different optical wavelengthsto use the different optical absorption behaviors of the blood for livefinger detection. When a person' heart beats, the pulse pressure pumpsthe blood to flow in the arteries, so the extinction ratio of thematerials being monitored in the blood changes with the pulse. Thereceived signal carries the pulse signals. These properties of the bloodcan be used to detect whether the monitored material is alive-fingerprint or a fake fingerprint.

FIG. 15 shows a comparison between optical signal behaviors in thereflected light from a nonliving material (e.g., a fake finger) and alive finger. The optical fingerprint sensor can also operate as aheartbeat sensor to monitor a living organism. When two or morewavelengths of the probe light are detected, the extinction ratiodifference can be used to quickly determine whether the monitoredmaterial is a living organism, such as live fingerprint. In the exampleshown in FIG. 15, probe light at different wavelengths were used, one ata visible wavelength and another an IR wavelength as illustrated in FIG.14.

When a nonliving material touches the top cover glass above thefingerprint sensor module, the received signal reveals strength levelsthat are correlated to the surface pattern of the nonliving material andthe received signal does not contain signal components associated with afinger of a living person. However, when a finger of a living persontouches the top cover glass, the received signal reveals signalcharacteristics associated with a living person, including obviouslydifferent strength levels because the extinction ratios are differentfor different wavelengths. This method does not take long time todetermine whether the touching material is a part of a living person. InFIG. 15, the pulse-shaped signal reflects multiple touches instead ofblood pulse. Similar multiple touches with a nonliving material does notshow the difference caused by a living finger.

This optical sensing of different optical absorption behaviors of theblood at different optical wavelengths can be performed in a shortperiod for live finger detection and can be faster than opticaldetection of a person's heart beat using the same optical sensor.

In LCD displays, the LCD backlighting illumination light is white lightand thus contains light at both the visible and IR spectral ranges forperforming the above live finger detection at the optical sensor module.The LCD color filters in the LCD display module can be used to allow theoptical sensor module to obtain measurements in FIGS. 14 and 15. Inaddition, the designated light sources 436 for producing theillumination light for optical sensing can be operated to emit probelight at the selected visible wavelength and IR wavelength at differenttimes and the reflected probe light at the two different wavelengths iscaptured by the optical detector array 621 to determine whether touchedobject is a live finger based on the above operations shown in FIGS. 14and 15. Notably, although the reflected probe light at the selectedvisible wavelength and IR wavelength at different times may reflectdifferent optical absorption properties of the blood, the fingerprintimage is always captured by both the probe light the selected visiblewavelength and the probe light at the IR wavelength at different times.Therefore, the fingerprint sensing can be made at both the visiblewavelength and IR wavelength.

FIG. 16 shows an example of an operation process for determining whetheran object in contact with the LCD display screen is part of a finger ofa live person by operating the one or more illumination light sourcesfor optical sensing to illuminate the finger with light in two differentlight colors.

For yet another example, the disclosed optical sensor technology can beused to detect whether the captured or detected pattern of a fingerprintor palm is from a live person's hand by a “live finger” detectionmechanism by other mechanisms other than the above described differentoptical absorptions of blood at different optical wavelengths. Forexample, a live person's finger tends to be moving or stretching due tothe person's natural movement or motion (either intended or unintended)or pulsing when the blood flows through the person's body in connectionwith the heartbeat. In one implementation, the optical sensor module candetect a change in the returned light from a finger or palm due to theheartbeat/blood flow change and thus to detect whether there is a liveheartbeat in the object presented as a finger or palm. The userauthentication can be based on the combination of the both the opticalsensing of the fingerprint/palm pattern and the positive determinationof the presence of a live person to enhance the access control. For yetanother example, as a person touches the LCD display screen, a change inthe touching force can be reflected in one or more ways, includingfingerprint pattern deforming, a change in the contacting area betweenthe finger and the screen surface, fingerprint ridge widening, or ablood flow dynamics change. Those and other changes can be measured byoptical sensing based on the disclosed optical sensor technology and canbe used to calculate the touch force. This touch force sensing can beused to add more functions to the optical sensor module beyond thefingerprint sensing.

In the above examples where the fingerprint pattern is captured on theoptical sensor array via an imaging module as in FIG. 4B and FIG. 6B,optical distortions tend to degrade the image sensing fidelity. Suchoptical distortions can be corrected in various ways. For example, aknown pattern can be used to generate an optical image at the opticalsensor array and the image coordinates in the know pattern can becorrelated to the generated optical image with distortions at theoptical sensor array for calibrating the imaging sensing signals outputby the optical sensor array for fingerprint sensing. The fingerprintsensing module calibrates the output coordinates referencing on theimage of the standard pattern.

In light of the disclosure in this patent document, variousimplementations can be made for the optical sensor module as disclosed.

For example, a display panel can be constructed in which each pixelemitting lights, and can be controlled individually; the display panelincludes an at least partially transparent substrate; and a coversubstrate, which is substantially transparent. An optical sensor moduleis placed under the display panel to sense the images form on the top ofthe display panel surface. The optical sensor module can be used tosense the images form from light emitting from display panel pixels. Theoptical sensor module can include a transparent block with refractiveindex lower than the display panel substrate, and an imaging sensorblock with an imaging sensor array and an optical imaging lens. In someimplementations, the low refractive index block has refractive index inthe range of 1.35 to 1.46 or 1 to 1.35.

For another example, a method can be provided for fingerprint sensing,where light emitting from a display panel is reflected off the coversubstrate, a finger placed on top of the cover substrate interacts withthe light to modulate the light reflection pattern by the fingerprint.An imaging sensing module under the display panel is used to sense thereflected light pattern image and reconstruct fingerprint image. In oneimplementation, the emitting light from the display panel is modulatedin time domain, and the imaging sensor is synchronized with themodulation of the emitting pixels, where a demodulation process willreject most of the background light (light not from pixels beingtargeted).

Various design considerations for the disclosed under-screen opticalsensor module for optical fingerprint sensing are further described inAttachment 3 entitled “MULTIFUNCTION FINGERPRINT SENSOR AND PACKAGING”(41 pages in text and 26 sheets of drawings) as part of U.S. ProvisionalPatent Application No. 62/289,328, and U.S. Provisional PatentApplication No. 62/330,833, and International Patent Application No.PCT/US2016/038445, filed on Jun. 20, 2016 (claiming priority from U.S.Provisional Patent Application No. 62/181,718, filed on Jun. 18, 2015,and published under No. WO 2016/205832 on Dec. 22, 2016), andInternational Patent Application No. PCT/CN2016/104354, filed on Nov. 2,2016 (claiming priority from U.S. Provisional Patent Application No.62/249,832, filed on Nov. 2, 2015, and published under No. WO2017/076292 on May 11, 2017). The entire disclosures of the abovementioned patent applications are incorporated by reference as part ofthe disclosure of this patent document.

In various implementations of the under-screen optical sensor moduletechnology for fingerprint sensing disclosed herein, the optical imagingof the illuminated touched portion of a finger to the optical sensorarray in the under-screen optical sensor module can be achieved withoutusing an imagine module such as a lens by imaging the returned lightfrom the touched portion of the finger under optical illumination. Onetechnical challenge for optical fingerprint sensing without an imagingmodule is how to control the spreading of the returned light that mayspatially scramble returned light from different locations on thetouched portion of the finger at the optical sensor array so that thespatial information of different locations may be lost when suchreturned light reaches the optical sensor array. This challenge can beaddressed by using optical collimators or an array of pinholes toreplace the optical imaging module in the under-screen optical sensormodule for detecting a fingerprint by optical sensing. A device forimplementing such optical fingerprint sending can include a devicescreen that provides touch sensing operations and includes a displaypanel structure having light emitting display pixels, each pixeloperable to emit light for forming a portion of a display image; a toptransparent layer formed over the device screen as an interface forbeing touched by a user for the touch sensing operations and fortransmitting the light from the display structure to display images to auser; and an optical sensor module located below the display panelstructure to receive light that is emitted by at least a portion of thelight emitting display pixels of the display structure and is returnedfrom the top transparent layer to detect a fingerprint, the opticalsensor module including an optical sensor array that receives thereturned light and an array of optical collimators or pinholes locatedin a path of the returned light to the optical sensor array. The arrayof optical collimators are used to collect the returned light from thedisplay panel structure and to separate light from different locationsin the top transparent layer while directing the collected returnedlight to the optical sensor array.

The imaging by using collimators relies on using different collimatorsat different locations to spatially separate light from differentregions of a fingerprint to different optical detectors in the opticaldetector array. The thickness or length of each collimator along thecollimator can be designed to control the narrow field of optical viewof each collimator, e.g., the light from only a small area on theilluminated finger is captured by each collimator and is projected ontoa few adjacent optical detectors in the optical detector array. As anexample, the thickness or length of each collimator along the collimatorcan be designed to be large, e.g., a few hundred microns, so that thefield of optical view of each collimator may allow the collimator todeliver imaging light to a small area on the optical detector array,e.g., one optical detector or a few adjacent optical detectors in theoptical detector array (e.g., an area of tens of microns on each side onthe optical detector array in some cases).

The following sections explain how an array of optical collimators orpinholes can be used for under-screen optical fingerprint sensing by theexamples for using optical collimators in optical fingerprint sensing inhybrid sensing pixels each having a capacitive sensor for capturingfingerprint information and an optical sensor for capturing fingerprintinformation.

FIGS. 17A and 17B show two examples of hybrid sensing pixel designs thatcombine capacitive sensing and optical sensing within the same sensingpixel.

FIG. 17A shows an example of a fingerprint sensor device 2100 thatincorporates a capacitive sensor in addition to an optical sensor foreach sensor pixel of an array of sensor pixels in capturing fingerprintinformation. By combining both capacitive sensors and optical sensors,fingerprint images obtained with the optical sensors can be used tobetter resolve the 3D fingerprint structure obtained with the capacitivesensors. For illustrative purposes, the structure shown in FIG. 17Arepresents one sensor pixel in an array of sensor pixels and each sensorpixel includes an optical sensor 2102 and a capacitive sensor 2114 thatare disposed next to each other within the same pixel.

The optical sensor 2102 includes a photodetector 2108 and a collimator2106 disposed over the photodetector 2108 to narrow or focus reflectedlight 2124 from finger 2102 toward the photodetector 2108. One or morelight sources, such as LEDs (not shown) can be disposed around thecollimator 2106 to emit light, which is reflected off the finger asreflected light 2124 and is directed or focused toward the correspondingphotodetector 2108 to capture a part of the fingerprint image of thefinger 2102. The collimator 2106 can be implemented using an opticalfiber bundle or one or more metal layer(s) with holes or openings. Thisuse of multiple optical collimators above the optical detector array maybe used as a lensless optical design for capturing the fingerprint imagewith a desired spatial resolution for reliable optical fingerprintssensing. FIG. 17A shows the collimator 2106 implemented using one ormore metal layers 2110 with holes or openings 2112. The collimator 2106in the layer between the top structure or layer 2104 and thephotodetectors 2108 in FIG. 17A includes multiple individual opticalcollimators formed by optical fibers or by holes or openings in one ormore layers (e.g., silicon or metal) and each of such individual opticalcollimators receives light ray 2124 in a direction along thelongitudinal direction of each optical collimator or within a smallangle range that can be captured by the top opening of each opening orhole and by the tubular structure as shown so that light rays incidentin large angles from the longitudinal direction of each opticalcollimator are rejected by each collimator from reaching the opticalphotodiode on the other end of the optical collimator.

In the capacitive sensing part of each sensing pixel, the capacitivesensor 2114 includes a capacitive sensor plate 2116 that iselectromagnetically coupled to a portion of a finger that is eithernearby or in contact with the sensing pixel to perform the capacitivesensing. More specifically, the capacitive sensor plate 2116 and thefinger 2102 interact as two plates of one or more capacitive elements2122 when the finger 2102 is in contact with or substantially near theoptional cover 2104 or a cover on a mobile device that implements thefingerprint sensor device 2100. The number of capacitive sensor plates2116 can vary based on the design of the capacitive sensor 2114. Thecapacitive sensor plate 2116 can be implemented using one or more metallayers. The capacitive sensor plate 2116 is communicatively coupled tocapacitive sensor circuitry 2120 so that the capacitive sensor circuitry2120 can process the signals from the capacitive sensor plate 2116 toobtain data representing the 3D fingerprint structure. A routing orshielding material can be disposed between the capacitive sensor plate2116 and the capacitive sensor circuitry to electrically shield themetal plate 2116. The capacitive sensor circuitry 2120 can becommunicatively coupled to both the capacitive sensor plate 2116 and thephotodetector 2108 to process both the signal from the capacitive sensorplate 2116 and the signal from the photodetector 2108. In FIG. 17A, thecapacitive sensor and the optical sensor within each hybrid sensingpixel are adjacent to and displaced from each other without beingspatially overlapped.

In implementations, the optical sensing features in the hybrid sensordesign in FIG. 17A such as the optical collimator design can be used ina under-screen optical sensor module. Therefore, the optical sensingwith the optical collimator feature in FIG. 17A may be implemented in amobile device or an electronic device is capable of detecting afingerprint by optical sensing to include a display screen structure; atop transparent layer formed over the display screen structure as aninterface for being touched by a user and for transmitting the lightfrom the display screen structure to display images to a user; and anoptical sensor module located below the display screen structure toreceive light that is returned from the top transparent layer to detecta fingerprint. The optical sensor module includes an optical sensorarray of photodetectors that receive the returned light and an array ofoptical collimators to collect the returned light from the toptransparent layer via the display screen structure and to separate lightfrom different locations in the top transparent layer while directingthe collected returned light through the optical collimators to thephotodetectors of the optical sensor array.

FIG. 17B illustrates another example of a fingerprint sensor device 2130that structurally integrates an optical sensor and a capacitive sensorin each hybrid sensor pixel in a spatially overlap configuration in anarray of sensor pixels to reduce the footprint of each hybrid sensingpixel. The fingerprint sensor device 2130 includes a semiconductorsubstrate 2131, such as silicon. Over the substrate 2131, multiplesensing elements or sensing pixels 2139 are disposed. Each sensingelement or sensing pixel 2139 includes active electronics circuitry area2132 including CMOS switches, amplifier, resistors and capacitors forprocessing sensor signals. Each sensing pixel or sensing element 2139includes a photodetector 2133 disposed or embedded in the activeelectronics circuitry area 2132. A capacitive sensor plate or a topelectrode 2134 of the capacitive sensor for capacitive sensing isdisposed over a photodetector 2133 and includes a hole or opening 2138on the sensor plate 2134 to function also as a collimator of light fordirecting light onto the photodetector 2133. A via 2135 filled withconductive material is disposed to electrically connect the topelectrode 2134 to the active circuit elements 2132. By adjusting theopening or the hole and the distance of the top electrode 2134 with thephotodetector 2133, the light collecting angle 2137 of the photodetector(e.g., photodiode) 2133 can be adjusted. The fingerprint sensor device2130 is covered by a protective cover 2136, which includes hardmaterials, such as sapphire, glass etc. Photodetector 2133 lightcollection angle 2137 can be designed to preserve the spatial resolutionof the image collected by the photodiode arrays. A light source 2140,such as an LED, is placed under the cover, on the side of fingerprintsensor device 2130 to emit light, which is reflected off the finger anddirected toward the photodetector 2133 to capture the fingerprint image.When a finger touches or comes substantially near the protective cover,the finger and the sensing top electrode 2134 in combination form acapacitive coupling (e.g., capacitor 2142) between the human body andsensing top electrode 2134. The fingerprint sensor device 2130 thatincludes both optical and capacitive sensors can acquire images of botha light reflection image of fingerprint and also a capacitive couplingimage. The sensing top electrode 2134 serves dual purpose: 1) forcapacitive sensing, and 2) as a collimator (by fabricating one or moreholes on the sensing top electrode 2134) to direct, narrow or focusreflected light from the finger toward the photodetector 2133. Reusingthe sensing top electrode 2134 eliminates the need for additional metallayer or optical fiber bundle, and thus reduces each pixel size andaccordingly the overall size of the fingerprint sensor device 2130.

In FIG. 17B, the optical sensing design uses the holes or openings 2138formed between the top layer 2136 and the bottom array of photodetectors2133 as an optical collimators to select only light rays within certainangles 2137 to preserve the spatial resolution of the image collected bythe photodetectors 2133 in the photodetector array as illustrated.Similar to the fiber or other tubular shaped optical collimators in FIG.17A, the holes or openings 2138 formed between the top layer 2136 andthe bottom array of photodetectors 2133 constitute optical collimatorsto collect the returned light from the top transparent layer via thedisplay screen structure and to separate light from different locationsin the top transparent layer while directing the collected returnedlight through the optical collimators to the photodetectors 2133.

FIG. 18 is a top-down view of an exemplary hybrid fingerprint sensordevice 2200 incorporating both an optical sensor and a capacitive sensorin each hybrid sensing pixel. The fingerprint sensor device 2200 isimplemented as a CMOS silicon chip 2221 that includes an array of hybrid(incorporating both an optical sensor and a capacitive sensor) sensingelements or pixels 2222. Alternatively, the optical layout in FIG. 18can also be for all optical sensing designs disclosed in this documentwhere the openings or holes 2223 represent the optical collimators inFIG. 17A or 17B. The size or dimension of the sensing elements can be inthe range of 25 μm to 250 μm, for example. The hybrid sensor device 2200can include an array of support circuitry including amplifiers, ADCs,and buffer memory in a side region 2224. In addition, the hybrid sensordevice 2200 can include an area for wire bonding or bump bonding 2225. Atop layer 2226 of the hybrid sensor element 2222 can include a metalelectrode for capacitive sensing. One or more openings or holes 2223 canbe fabricated on each top metal electrode 23 to structurally serve as acollimator for directing light in a vertical direction to shine on aphotodetector under the top electrode. Thus, the top layer 2226structure can serve dual purposes of optical and capacitive sensing. Asensor device processor can be provided to process the pixel outputsignals from hybrid sensing pixels to extract the fingerprintinformation.

In addition to sharing the same structure for capacitive sensing and forfocusing light in the vertical direction as a collimator, one instanceof sensor signal detection circuitry can be shared between the opticaland capacitive sensors to detect the sensor signals from both aphotodetector and a capacitive sensor plate.

FIG. 19A illustrates a circuit diagram for an exemplary hybridfingerprint sensing element or pixel 2300 having both capacitive sensingand optical sensing functions for fingerprints. The exemplary sensorpixel 2300 includes sensor signal detection circuitry 2316 toselectively switch between detecting or acquiring sensor signals from asensing top electrode (e.g., a top metal layer) 2308 based on capacitivesensing and a photodetector (e.g., a photodiode) 2314 based on opticalsensing to acquire both a reflective optical image from thephotodetector 2314 and a capacitive coupled image from the capacitivesensor electrode 2308 from a finger. In some implementations, the twoimages from the two sensing mechanisms in each hybrid sensing pixel canbe serially processed by the sensor signal detection circuitry. In theillustrated example, switches 2310 and 2312 have first terminals thatare electrically coupled to the sensing top electrode 2308 and thephotodetector 2314, respectively, and second terminals that are coupledto a common input terminal of the sensor signal detection circuitry 2316to provide corresponding optical detector signal from the photodetector2314 and the corresponding capacitive sensing signal from the sensingtop electrode 2308 to the sensor signal detection circuitry 2316. Whenthe switch 2310 is turned off (CAP_EN=0) and the switch 2312 is turnedon (Optical_en=1), the sensor signal detection circuitry 2316 acquiresthe optical detector signal representing the optical image of thescanned fingerprint received at the particular hybrid sensing pixel. Thesensor signal detection circuitry 2316 can acquire the capacitivesensing signal representing the capacitive image of the scannedfingerprint when switch 2310 CAP_EN=1 and Optical_en=0. After both theoptical and capacitive images are acquired, both images can be processedin downstream circuitry separately and in combination to identify thefingerprint characteristics.

With the two modality of imaging by the above hybrid sensing pixels, theperformance of the fingerprint identification can be enhanced by makinguse of the two types of the images in different ways. This enhancedfingerprint identification can be achieved by the sensor deviceprocessor, such as sensor device processor 2321, for processing thepixel output signals from the hybrid sensing pixels to extract thefingerprint information. For example, the capacitive image can provide a3D image on the depth of the ridges and valleys of the fingerprintfeatures. Complementing the 3D capacitive image, the optical image canprovide a high resolution 2D information on the fingerprintcharacteristics. The optical 2D image having a higher spatial resolutioncan be used to recover the capacitive sensing image resolution becauseboth images information on the same ridges of the fingerprint. In someimplementations where the capacitive sensing method may be moresensitive and accurate on identifying the valleys of the fingerprintthan the optical sensing method, the spatial resolution of imagesacquired using the capacitive sensing method can degrade based on thethickness of the cover. This aspect of the capacitive sensing can besupplemented by the optical sensing. In operation, the sensor responsemay be fixed and the point spread function of the capacitive sensor maybe fixed for all sensor positions. The higher resolution optical sensingcan be used as a resolution recovery method and can be applied on thecapacitive sensing image to enhance the 3D image. A partial highresolution image from optical sensing can be available to help with therecovering method. Thus, the 3D capacitive image can be enhanced toprovide more information on the valleys and ridges by interpolating orrecovering based on the high resolution 2D image.

The enhanced 3D image can provide an improved fingerprint recognitionand matching. In another example, the optical and capacitive images canbe stored together to provide two comparisons each time a fingerprintrecognition or matching is performed. The use of two types of images forcomparison enhances the accuracy and security of the fingerprint sensingsystem.

The sensor signal detection circuitry 2316 can be implemented in variousways using a number different circuitry designs. In one example,integrator sensing circuitry 2318 can be implemented to store theelectric charges caused by ridges and valleys touching or beingsubstantially near the cover of the fingerprint sensor device of thecover of the mobile device. The inclusion of the integrator circuitry2318 enhances the signal-to-noise ratio (SNR). The integrator sensingcircuitry includes an operational amplifier 2322 to amplify a sensorsignal, such as a capacitance related or optical related signal (e.g.,voltage signal), detected by the sensing top electrode 2308 or thephotodetector 2314 of the exemplary sensor pixel 2300. The sensing topelectrode 2308 that include a conductive material, such as one of avariety of metals is electrically connected to a negative or invertingterminal 2328 of the amplifier 2322 through the switch 2310. The sensingtop electrode 2108 and a local surface of the finger 2302 function asopposing plates of a capacitor Cf 2302. The capacitance of the capacitorCf 2302 varies based on a distance ‘d’ between the local surface of thefinger and the sensing top electrode 2308, the distance between the twoplates of the capacitor Cf 2302. The capacitance of capacitor Cf 2302 isinversely proportional to the distance ‘d’ between the two plates of thecapacitor Cf 2302. The capacitance of capacitor Cf 2302 is larger whenthe sensing top electrode 2308 is opposite a ridge of the finger thanwhen opposite a valley of the finger.

In addition, various parasitic or other capacitors can be formed betweendifferent conductive elements in the exemplary sensor pixel 2300. Forexample, a parasitic capacitor CP 2304 can form between the sensing topelectrode 2308 and a device ground terminal 2305. Device ground iscoupled to earth ground closely. Another capacitor Cr 2324 can formbetween an output conductor of the amplifier 2322 and the negative orinverting terminal 2328 of the amplifier 2322 and functions as afeedback capacitor to the amplifier 2322. Also, a switch 2326 can becoupled between the output of the amplifier 2322 and the negative orinverting terminal 2328 of the amplifier 2322 to reset the integratorcircuitry 2318.

The positive terminal of the amplifier 2322 is electrically connected toan excitation signal Vref. The excitation signal Vref can be directlyprovided to the positive terminal of a dedicated amplifier in eachsensor pixel. By providing the excitation signal Vref directly to thepositive terminal of the amplifier 2322, the exemplary sensor pixel 2100becomes an active sensor pixel. In addition, providing the excitationsignal Vref directly to the positive terminal of the amplifier 2322eliminates the need to include an excitation electrode, common to allsensor pixels, which reduces a conductive (e.g., metal) layer from thesemiconductor structure of the sensor chip. In some implementations, anoptional excitation electrode 2306 can be implemented to enhance the SNRbased on the design of the sensor pixel. In addition, by providing theexcitation signal Vref 2330 directly to the amplifier 2322, theexcitation signal Vref 2322 is not applied directly to the finger toavoid potentially irritating or injuring the finger. Moreover, when theexcitation electrode for applying the excitation signal directly to thefinger is not used, all components of the fingerprint sensor device canbe integrated into a single packaged device, and the entire fingerprintsensor device can be disposed under the protective cover glass. With theentire fingerprint sensor device disposed under the protective coverglass, the fingerprint sensor device is protected from the finger andother external elements that can potentially damage the fingerprintsensor.

In FIG. 19A, the output signal (optical and capacitive) of the sensorsignal detection circuitry 2316 (e.g., Vpo of the amplifiers 2322) inthe sensor pixels 2300 is electrically coupled to a switch 2320 toselectively output the output signal Vpo from the sensor pixel 2300 to asignal processing circuity including a filter. The switch 2320 can beimplemented using a transistor or other switching mechanisms andelectrically coupled to a controller to control the switching of theswitch 2320. By controlling the switches 2320, 2310 and 2312, the sensorpixels in an array of sensor pixels can be selectively switched betweenacquiring the optical signals and the capacitive signals. In oneimplementation, the optical or capacitive signal can be acquired foreach line, row or column of sensor pixels in the array and then switchedto acquire the other type of signal for the line, row or column. Theswitching between the optical and capacitive signal acquisition can beperformed line-by-line. In another implementation, one type of signal(capacitive or optical) can be acquired for all sensor pixels orelements in the array and then switched to acquire the other type ofsignal for all of the sensor pixels or elements. Thus, the switchingbetween acquisition of different signal types can occur for the entirearray. Other variations of switching between acquisition of the twotypes of sensor signals can be implemented.

FIG. 19B illustrates a circuit diagram for another exemplary hybridfingerprint sensing element or pixel 2340. The hybrid fingerprintsensing element or pixel 2340 is substantially the same as the hybridfingerprint sensing element or pixel 2300 with respect to the componentshaving the same reference number. For descriptions of the commoncomponents having the same reference number, refer to the description ofFIG. 19A.

The hybrid fingerprint sensing element or pixel 2340 implements thesensing top electrode 2308 to include a hole or opening 2342 thatfunctions as a collimator to focus or narrow the reflected light 2344toward the photodetector 2314 (e.g., photodiode). The photodetector 2314can be positioned or disposed below the collimator implemented using thesensing top electrode 2308 to capture the reflected light 2344 focusedby the collimator 2308.

In some implementations, separate instances of sensor signal detectioncircuitry can be included for the optical and capacitive sensors todetect in parallel the sensor signals from both a photodetector and acapacitive sensor plate.

FIG. 19C illustrates a circuit diagram of an exemplary hybridfingerprint sensing element or pixel 2350 for performing paralleldetection of sensor signals from the photodetector and the capacitivesensor plate. The hybrid fingerprint sensing element or pixel 2350 issubstantially the same as the hybrid fingerprint sensing element orpixel 2340 with respect to the components having the same referencenumber. For descriptions of the common components having the samereference number, refer to the description of FIG. 19A.

To perform sensor signal detection from both the capacitive plate andthe photodetector in parallel, the hybrid fingerprint sensing element orpixel 2350 includes separate sensor signal detection circuitry 2316 and2317 communicatively coupled to the sensing top electrode 2308 and thephotodetector 2324 respectively. Sensor signal detection circuitry 2317can be implemented to be substantially similar to sensor signaldetection circuitry 2316. In some implementations, switches 2310 and2312 can be disposed to have first terminals that are electricallycoupled to the sensing top electrode 2308 and the photodetector 2314,respectively, and second terminals that are coupled to respective sensorsignal detection circuitry 2316 and 2317 to provide the optical detectorsignal from the photodetector 2314 and the capacitive sensing signalfrom the sensing top electrode 2308 to the sensor signal detectioncircuitry 2316 and 2317 respectively When the switches 2310 and 2312 areturned on and off together, the sensor signal detection circuitry 2316and 2317 can perform sensor signal detection from the capacitive plate2308 and the photodetector 2314 in parallel. When the switches 2310 and2312 are turned on and off out of phase with each other, the sensorsignal detection circuitry 2316 and 2317 can perform sensor signaldetection from the capacitive plate 2308 and the photodetector 2314 inseries. In addition, the sensor device processor 2321 can becommunicatively coupled to the sensor signal detection circuitry 2316and 2317 either directly or indirectly through switches 2320A and 2320Bto process the detected sensor signals from the capacitive plate 2308and the photodetector 2314 in parallel or in series.

In another aspect of the disclosed technology, the optical sensordescribed with respect to FIGS. 17A, 17B, 18, 19A and 19B can be used tomeasure human heart beat by measuring the reflected light intensitychange with time caused by blood flow variations in fingers due to theheart beat and pumping actions of the heart. This information iscontained in the received light that is reflected, scattered or diffusedby the finger and is carried by the optical detector signal. Thus, theoptical sensor can serve multiple functions including acquiring anoptical image of the fingerprint and to measure human heart beat. Inimplementations, a sensor device processor is used to process one ormore optical detector signals to extract the heart beat information.This sensor device processor may be the same sensor device processorthat processes the pixel output signals from optical sensing pixels orhybrid sensing pixels to extract the fingerprint information.

The following sections describe examples of various designs forfingerprint sensing using a under-screen optical sensor module using anarray of optical collimators or pinholes for directing signal lightcarrying fingerprint information to the optical sensor array. Suchoptical collimators or pinholes are placed between the LCD displayscreen and the optical sensor array in the under-screen optical sensormodule to couple desired returned light from the display panel whilefiltering out background light in the optical detection by the opticalsensor array. Implementation of such optical collimators or pinholes cansimplify the optical designs of the optical detection by the opticalsensor array, e.g., without using complex optical imaging designs inother designs disclosed in this patent document, such as the imagingdesigns in FIGS. 6B, 7, 10A, and 11. In addition, implementation of suchoptical collimators or pinholes can simplify the optical alignment ofthe overall optical layout to the optical sensor array and improvereliability and performance of the optical detection by the opticalsensor array. Furthermore, such optical collimators or pinholes cansignificantly simplify the fabrication and reduce the overall cost ofthe under-screen optical sensor module.

FIG. 20 shows an example of a smartphone having a liquid crystal display(LCD) display and an under-screen optical sensor module that includes anoptical collimator array for collecting and directing light to anoptical detector array for optical fingerprint sensing. The LCD-basedtouch sensing display system 423 implements an optical sensing modulewith a photo detector array 621 under the LCD display system 423.

The touch sensing display system 423 is placed under a top cover glass431 which serves as a user interface surface for various userinterfacing operations, including, e.g., touch sensing operations by theuser, displaying images to the user, and an optical sensing interface toreceive a finger for optical fingerprint sensing and other opticalsensing operations where probe light is directed from inside the deviceto the top cover glass 431 to illuminate the finger. The display system423 is a multi-layer LCD module 433 that includes LCD displaybacklighting light sources 434 (e.g., LED lights) that provide the whitebacklighting for the LCD module 433, a light waveguide layer 433 ccoupled to the LCD display backlighting light sources 434 to receive andguide the backlighting light, LCD structure layers 433 a (including,e.g., a layer of liquid crystal (LC) cells, LCD electrodes, transparentconductive ITO layer, an optical polarizer layer, a color filter layer,and a touch sensing layer), a backlighting diffuser 433 b placedunderneath the LCD structure layers 433 a and above the light waveguidelayer 433 c to spatially spread the backlighting light for illuminatingthe LCD display pixels in the LCD structure layers 433 a, and an opticalreflector film layer 433 d underneath the light waveguide layer 433 c torecycle backlighting light towards the LCD structure layers 433 a forimproved light use efficiency and the display brightness. When the LCDcells in the sensing window are turned on, most of the LCD structurelayers 433 a (include liquid crystal cells, electrodes, transparent ITO,polarizer, color filter, touch sensing layer etc.) become partiallytransparent although the micro structure may extinct partial of theprobe light energy. The light diffuser 433 b, the light waveguide 433 c,the reflector film 433 d, and the LCD module frame are treated to holdthe fingerprint sensor and provide transparent or partially transparentsensing light path so that a portion of the reflected light from the topsurface of the cover glass 431 can reach a photo detector array 621 withan under-LCD-screen optical sensor module for fingerprint sensing andother optical sensing operations. As illustrated, this optical sensormodule under the LCD screen includes various fingerprint sensor parts,e.g., an optical collimator array 617 for collimating and directingreflected probe light to the photo detector array 621, and an opticalsensor circuit module 623 that receives and conditions the detectoroutput signals from the photo detector array 621. The optical collimatorarray 617 can include optical collimators and may be a waveguide basedimage transmitter, an optical fiber array, a micro lens array, or apinhole array. The optical collimators operate to limit the numeralaperture (NA) of the sampling image and to form corresponding imageelements. Each optical collimator unit gets a part of the image of thetouched portion of a target finger on the top glass cover 431. Thetransmitted light beams of all the collimators collectively form a fullimage of the target at the photo detector array 621. The photodiodearray 621 may be a CMOS sensor of CMOS sensing pixels, a CCD sensorarray or a suitable optical sensor array that is sensitive to light.

The example illustrates includes an electronics module 435 for the LCDdisplay and touch sensing operations, one or more other sensors 425 suchas an optical sensor for monitoring the light level of the surroundings,optional side buttons 427 and 429 for controls of certain smartphoneoperations.

In the example in FIG. 20, the light sources in the illustrated exampleinclude the display back lighting light sources 434 and the extradesignated probe light sources 436. The light beams 442 a from extradesignated probe light sources 436 and the light beams 442 b from thedisplay light sources 434 can be used as the sensor probe light forilluminating a finger in contact with the top glass cover 431 togenerate the desired reflected probe light carrying the fingerprintpattern and other information to the optical sensor module.

When the LCD cells in the sensing window are turned on, most of the LCDstructure layers 433 a (include liquid crystal cells, electrodes,transparent ITO, polarizer, color filter, touch sensing layer etc.)become partially transparent although the micro structure may extinctpartial of the probe light energy. The light diffuser 433 b, the lightwaveguide 433 c, the reflector film 433 d, and the LCD module frame aretreated to hold the fingerprint sensor and provide transparent orpartially transparent sensing light path.

FIG. 21 below further illustrates the operation of the under LCD screenoptical sensor module in the above example in FIG. 20. On the top coverglass 431, a fingerprint sensing area or window is an area on the topsurface of the top cover glass 431 that is right above or near theunderlying optical sensor module. Since the optical sensor module isunderneath the LCD structure, The sensing window is part of thecontiguous top surface of the top cover glass 431 and is also part ofthe display area for the LCD display. Accordingly, there may be novisible physical demarcation on the top surface to indicate this sensingwindow. This sensing window may be indicated to a user via other meansto assist the user to place a finger within the sensing window forfingerprint sensing and other optical sensing operations. For example,the extra designated probe light sources 436 may be used to illuminatethe sensing window so that the area for the sensing window is distinctlydifferent from the surrounding areas on the top cover glass and isreadily visible to the user. This can be done when the LCD panel isturned off or when the LCD panel is turned on.

As shown in FIG. 21, a user presses a finger on the sensing window andthe probe light beam 82P illuminates the finger. The finger and thecover glass 431 reflect the probe light as a reflected signal light beam82R. Various scattering interfaces 433S in the LCD module 433 diffusesthe reflected signal light beam 82R to form diffused light beam 82D.Individual collimator units in the collimator array 617 select lightcomponent 82S and guide the selected light component 82S intocorresponding photosensing detectors of the photodetector array 621. Thephotosensing detectors, e.g., photodiodes or CMOS sensing detectors,generate corresponding sensor signals that contain information on thefingerprint pattern. A portion of the source light may enter thefingerprint sensor module without first going through the finger sensingarea on the top surface of the LCD panel. This part of light contributesbackground noise and can be eliminated by calibration. Each collimatorunit of the collimator array 617 only selects the light be transmittedalong its permitted direction at a relatively low optical loss tocorresponding photo detectors in a part of the photodetector array 621.Accordingly, each collimator unit in the collimator array 617 and itscorresponding photo detectors in the photodetector array 621 operatetogether to define the effective detecting optical numeral aperture NA.This NA directly defines the spatial resolution of the image produced bythe optical sensor module.

Based on the disclosed under LCD screen optical sensing designs, aperson's finger, either in direct touch with the LCD display screen orin a near proximity about the LCD display screen, can produce thereturned light back into the LCD display screen while carryinginformation of a portion of the finger illuminated by the light outputby the LCD display screen. Such information may include, e.g., thespatial pattern and locations of the ridges and valleys of theilluminated portion of the finger. Accordingly, the optical sensormodule can be integrated to capture at least a portion of such returnedlight to detect the spatial pattern and locations of the ridges andvalleys of the illuminated portion of the finger by optical imaging andoptical detection operations. The detected spatial pattern and locationsof the ridges and valleys of the illuminated portion of the finger canthen be processed to construct a fingerprint pattern and to performfingerprint identification, e.g., comparing with a stored authorizeduser fingerprint pattern to determine whether the detected fingerprintis a match as part of a user authentication and device access process.This optical sensing based fingerprint detection by using the disclosedoptical sensor technology uses the LCD display screens as an opticalsensing platform and can be used to replace existing capacitivefingerprint sensors or other fingerprint sensors that are basicallyself-contained sensors as “add-on” components without using light fromdisplay screens or using the display screens for fingerprint sensing formobile phones, tablets and other electronic devices.

Notably, an optical sensor module based on the disclosed optical sensortechnology can be coupled to the backside of the LCD display screenwithout requiring a designated area on the display surface side of theLCD display screen that would occupy a valuable device surface realestate in some electronic devices such as a smartphone, a tablet or awearable device. Such an optical sensor module can be placed under theLCD display screen that vertically overlaps with the display screenarea, and, from the user's perspective, the optical sensor module ishidden behind the display screen area. In addition, because the opticalsensing of such an optical sensor module is by detecting the light fromthe LCD display screen and is returned from the top surface of thedisplay area, the disclosed optical sensor module does not require aspecial sensing port or sensing area that is separate from the displayscreen area. Accordingly, different from fingerprint sensors in otherdesigns, including, e.g., Apple's iPhone/iPad devices or Samsung Galaxysmartphone models where the fingerprint sensor is located at aparticular fingerprint sensor area or port (e.g., the home button) onthe same surface of the display screen but located in a designatednon-displaying zone that is outside the display screen area, the opticalsensor module based on the disclosed optical sensor technology can beimplemented in ways that would allow fingerprint sensing to be performedat any location on the LCD display screen by using unique opticalsensing designs by routing the returned light from the finger into anoptical sensor and by providing proper optical imaging mechanism toachieve high resolution optical imaging sensing. In this regard, thedisclosed optical sensor technology provides a unique on-screenfingerprint sensing configuration by using the same top touch sensingsurface that displays images and provides the touch sensing operationswithout a separate fingerprint sensing area or port outside the displayscreen area.

In addition to fingerprint detection by optical sensing, the opticalsensing may be used to measure other parameters. For example, thedisclosed optical sensor technology can measure a pattern of a palm of aperson given the large touch area available over the entire LCD displayscreen (in contrast, some designated fingerprint sensors such as thefingerprint senor in the home button of Apple's iPhone/iPad devices havea rather small and designated off-screen fingerprint sensing area thatis highly limited in the sensing area size not suitable for sensinglarge patterns). For yet another example, the disclosed optical sensortechnology can be used not only to use optical sensing to capture anddetect a pattern of a finger or palm that is associated with a person,but also to use optical sensing or other sensing mechanisms to detectwhether the captured or detected pattern of a fingerprint or palm isfrom a live person's hand by a “live finger” detection mechanism basedon the fact that a live person's finger tends to be moving or stretchingdue to the person's natural movement or motion (either intended orunintended) or pulsing when the blood flows through the person's body inconnection with the heartbeat. In one implementation, the optical sensormodule can detect a change in the returned light from a finger or palmdue to the heartbeat/blood flow change and thus to detect whether thereis a live heartbeat in the object presented as a finger or palm. Theuser authentication can be based on the combination of the both theoptical sensing of the fingerprint/palm pattern and the positivedetermination of the presence of a live person to enhance the accesscontrol. For yet another example, the optical sensor module may includea sensing function for measuring a glucose level or a degree of oxygensaturation based on optical sensing in the returned light from a fingeror palm. As yet another example, as a person touches the LCD displayscreen, a change in the touching force can be reflected in one or moreways, including fingerprint pattern deforming, a change in thecontacting area between the finger and the screen surface, fingerprintridge widening, or a blood flow dynamics change. Such changes can bemeasured by optical sensing based on the disclosed optical sensortechnology and can be used to calculate the touch force. This touchforce sensing adds more functions to the optical sensor module beyondthe fingerprint sensing.

With respect to useful operation or control features in connection withthe touch sensing aspect of the LCD display screen, the disclosedoptical sensor technology can provide triggering functions or additionalfunctions based on one or more sensing results from the optical sensormodule to perform certain operations in connection with the touchsensing control over the LCD display screen. For example, the opticalproperty of a finger skin (e.g., the index of refraction) tends to bedifferent from other artificial objects. Based on this, the opticalsensor module may be designed to selectively receive and detect returnedlight that is caused by a finger in touch with the surface of the LCDdisplay screen while returned light caused by other objects would not bedetected by the optical sensor module. This object-selective opticaldetection can be used to provide useful user controls by touch sensing,such as waking up the smartphone or device only by a touch via aperson's finger or palm while touches by other objects would not causethe device to wake up for energy efficient operations and to prolong thebattery use. This operation can be implemented by a control based on theoutput of the optical sensor module to control the waking up circuitryoperation of the LCD display screen which, for example, may includedesigned extra light sources for optical sensing and the designed extralight sources may turned on in a flash mode to intermittently emit flashlight to the screen surface for sensing any touch by a person's fingeror palm while the LCD display screen can be placed in a sleep mode tosave power. In some implementations, the wake-up sensing light can be inthe infrared invisible spectral range so a user will not experience anyvisual of a flash light.

An optical sensor module based on the disclosed optical sensortechnology can be coupled to the backside of the LCD display screenwithout requiring creation of a designated area on the surface side ofthe LCD display screen that would occupy a valuable device surface realestate in some electronic devices such as a smartphone, a tablet or awearable device. This aspect of the disclosed technology can be used toprovide certain advantages or benefits in both device designs andproduct integration or manufacturing.

In some implementations, an optical sensor module based on the disclosedoptical sensor technology can be configured as a non-invasive modulethat can be easily integrated to a LCD display screen without requiringchanging the design of the LCD display screen for providing a desiredoptical sensing function such as fingerprint sensing. In this regard, anoptical sensor module based on the disclosed optical sensor technologycan be independent from the design of a particular LCD display screendesign due to the nature of the optical sensor module: the opticalsensing of such an optical sensor module is by detecting the light fromthe LCD display screen and is returned from the top surface of thedisplay area, and the disclosed optical sensor module is coupled to thebackside of the LCD display screen for receiving the returned light fromthe top surface of the display area and thus does not require a specialsensing port or sensing area that is separate from the display screenarea. Accordingly, such an optical sensor module can be used to combinewith LCD display screens to provide optical fingerprint sensing andother sensor functions on a LCD display screen without using a speciallydesigned LCD display screen with hardware especially designed forproviding such optical sensing. This aspect of the disclosed opticalsensor technology enables a wide range of LCD display screens to be usedin smartphones, tablets or other electronic devices with enhancedfunctions from the optical sensing of the disclosed optical sensortechnology.

For example, for an existing phone assembly design that does not providea separate fingerprint sensor as in the Apple iPhones or Samsung models,such an existing phone assembly design can integrate the under-screenoptical sensor module as disclosed herein without changing the touchsensing-display screen assembly to provide an added on-screenfingerprint sensing function. Because the disclosed optical sensing doesnot require a separate designated sensing area or port as in the case ofthe Apple iPhones/Samsung phones with a front fingerprint senor outsidethe display screen area, or some smartphones with a designated rearfingerprint sensor on the backside like in some models by Huawei,Xiaomi, Google or Lenovo, the integration of the on-screen fingerprintsensing disclosed herein does not require a substantial change to theexisting phone assembly design or the touch sensing display module thathas both the touch sensing layers and the display layers. Simply put, noexternal sensing port and no extern hardware button are needed on theexterior of a device are needed for adding the disclosed optical sensormodule for fingerprint sensing. The added optical sensor module and therelated circuitry are under the display screen inside the phone housingand the fingerprint sensing is conveniently performed on the same touchsensing surface for the touch screen.

For another example, due to the above described nature of the opticalsensor module for fingerprint sensing, a smartphone that integrates suchan optical sensor module can be updated with improved designs, functionsand integration mechanism without affecting or burdening the design ormanufacturing of the LCD display screens to provide desired flexibilityto device manufacturing and improvements/upgrades in product cycleswhile maintain the availability of newer versions of optical sensingfunctions to smartphones, tablets or other electronic devices using LCDdisplay screens. Specifically, the touch sensing layers or the LCDdisplay layers may be updated in the next product release without addingany significant hardware change for the fingerprint sensing featureusing the disclosed under-screen optical sensor module. Also, improvedon-screen optical sensing for fingerprint sensing or other opticalsensing functions by such an optical sensor module can be added to a newproduct release by using a new version of the under-screen opticalsensor module without requiring significant changes to the phoneassembly designs, including adding additional optical sensing functions.

The above and other features of the disclosed optical sensor technologycan be implemented to provide a new generation of electronic deviceswith improved fingerprint sensing and other sensing functions,especially for smartphones, tablets and other electronic devices withLCD display screens to provide various touch sensing operations andfunctions and to enhance the user experience in such devices.

The optical sensor technology disclosed herein uses the light fordisplaying images in a display screen that is returned from the topsurface of the device display assembly for fingerprint sensing and othersensing operations. The returned light carries information of an objectin touch with the top surface (e.g., a finger) and the capturing anddetecting this returned light constitute part of the designconsiderations in implementing a particular optical sensor modulelocated underneath the display screen. Because the top surface of thetouch screen assembly is used as a fingerprint sensing area, the opticalimage of this touched area should be captured by an optical imagingsensor array inside the optical sensor module with a high image fidelityto the original fingerprint for robust fingerprint sensing. The opticalsensor module can be designed to achieve this desired optical imaging byproperly configuring optical elements for capturing and detecting thereturned light.

FIGS. 22A-22B show an exemplary implementation of the optical collimatordesign in FIGS. 20 and 21. The optical collimator array 2001 in thisexample includes an array of optical collimators 903 and an opticalabsorption material 905 filled between the optical collimators 903 toabsorb light to reduce cross talk between different optical collimators.Each collimator 903 of the collimator array 2001 may be channels thatare extended or elongated along a direction perpendicular to the displaypanel and lets the light be transmitted along its axis with a low loss.The collimator array 2001 is designed to reduce optical crosstalkbetween different optical collimators and to maintain a desired spatialresolution in the optical sensing. In some implementations, one opticalcollimator may correspond to only one photodetector in the photodetectorarray 2002. In other implementations, one optical collimator maycorrespond to two or more photodetectors in the photodetector array2002. As illustrated in FIG. 22B, the axis of each collimator unit maybe perpendicular to the display screen surface in some designs and maybe slanted with respect to the display surface. In operation, only thelight that propagates along a collimator axis carries the imageinformation. For example, the proper incident light 82P is reflected toform light 82R. Light 82R is then diffracted by the small holes of theTFT and expanded to light 82D. The light portion 82S is transmitted intothe photodiode array 2002. The light portion 82E away from the axis isabsorbed by the filling material. The reflectance on the cover glasssurface 431 carries the fingerprint information. Light rays 901 at anangle with respect to the collimator unit axis and thus may be blocked.A part of the reflected light, such as 901E, transmits into acorresponding optical collimator to reach the photodetector array 2002.

The optical collimator array can be made by different techniques,including, e.g., etching holes through a flat substrate, forming a lightwaveguide array, forming a micro lens array matching with opticalfilters, using coreless optical fiber bundle, or printing collimators ona transparent sheet. The desired features for such a collimator arrayinclude: (1) sufficient transmission contrast between the lightcomponent that propagates along the axis and the component thatpropagates off the axis so that the collimators ensures the desiredspatial resolution in the optical sensing of the fingerprint pattern atthe photodetector array; (2) the permitted transmission numericalaperture be sufficiently small to realize a desired high spatialresolution for the optical sensing.

Various optical collimator array designs may be used. Each opticalcollimator in the optical collimator array is structured to performspatial filtering by transmitting light in directions along or close toan axis of the optical collimator while blocking light in otherdirections and to have a small optical transmission numerical apertureto achieve a high spatial resolution by the array of opticalcollimators. The small optical transmission numerical aperture alsoreduces the amount of the background light that enters the opticalsensor array. The collimator element aperture and the pitch (i.e., thedistance between two nearby collimator elements) can be designed toachieve a desired spatial resolution for the optical fingerprintsensing.

FIG. 23 shows an example of a collimator design that is part of a CMOSstructure by using aligned holes in two different metal layers in theCMOS structure. Each optical collimator in the array is an elongatedchannel along a direction that is perpendicular to the display panel inthis particular example.

FIG. 24 shows an example of an optical fingerprint sensor module under aLCD display structure that incorporates an optical sensor array and anintegrated collimator array for each optical sensor pixel in capturingfingerprint information. The optical sensor array includes an array ofphotodetectors and a collimator array is disposed over the photodetectorarray to include optically transparent vias as optical collimators andoptically opaque metal structures between the vias as shown.Illumination light is directed to illuminate the touched portion of afinger and the light reflected off the finger is directed through theoptical collimator array to reach the photodetector array which capturesa part of the fingerprint image of the finger. The optical collimatorarray can be implemented using one or more metal layer(s) with holes oropenings integrated via the CMOS process.

Such optical collimators in the under-screen optical sensor module canbe structured to provide direct point to point imaging. For example, thedimensions of the optical collimator array and individual collimatorscan be designed to closely match the dimensions of the photodetectorarray and the dimensions of individual photodetectors, respectively, toachieve one to one imaging between optical collimators andphotodetectors. The entire image carried by the light received by theoptical sensor module can be captured by the photodetector array atindividual photodetectors simultaneously without stitching.

The spatial filtering operation of the optical collimator array canadvantageously reduce the amount of the background light that enters thephotodetector array in the optical sensor module. In addition, one ormore optical filters may be provided in the optical sensor module tofilter out the background light and to reduce the amount of thebackground light at the photodetector array for improved optical sensingof the returned light from the fingerprint sensing area due to theillumination by emitted light from the OLED pixels. For example, the oneor more optical filters can be configured, for example, as bandpassfilters to allow transmission of the illumination light generated foroptical sensing while blocking other light components such as the IRlight in the sunlight. This optical filtering can be an effective inreducing the background light caused by sunlight when using the deviceoutdoors. The one or more optical filters can be implemented as, forexample, optical filter coatings formed on one or more interfaces alongthe optical path to the photodetector array in the optical sensor moduleor one or more discrete optical filters.

FIG. 25 shows an example an optical collimator array with opticalfiltering to reduce background light that reaches the photodetectorarray in the under-screen optical sensor module. This example uses anarray of optical waveguides as the optical collimators and one or moreoptical filter films are coupled to the optical waveguide array toreduce undesired background light from reaching the photodetector arraycoupled to the optical waveguide array, e.g. the IR light from thesunlight while transmitting desired light in a predetermined spectralband for the probe light that is used to illuminate the finger. Theoptical waveguide can include a waveguide core with or without anoutside waveguide cladding. The optical waveguide may also be formed bya coreless fiber bundle with different fibers where each unit collimatoris a piece of fiber without a fiber core structure. When the corelessfibers are made into bundle, the filling material between the fibers mayinclude a light absorbing material so as to increase the absorption ofstray light that is not guided by the coreless fibers. The finalcollimator may be assembled with multiple layers of sub-collimatorarrays.

The following sections provide examples of various optical collimatordesigns and their fabrication.

FIGS. 26A and 26B show examples of fabricating collimators by etching.In FIG. 26A, a layer of a suitable material for forming opticalcollimators in the collimator array is formed on or supported by asupport substrate which is optically transparent. An etching mask isformed over the layer and has a pattern for etching the underlying layerto form the optical collimators. A suitable etching process is performedto form the optical collimators. The support substrate may be bound withthe collimator array and may be formed from various optical transparentmaterials including, e.g., silicon oxide.

FIG. 26B shows an example of an optical collimator array that isassembled by stacking multiple layers of sub-collimator arrays via aninter-layer connector material which may be an adhesive, a glass, or asuitable optically transparent material. In some implementations,different layers of sub-collimator arrays may be stacked over oneanother without the inter-layer connector material. This stacking allowsfabrication of optical collimators with desired lengths or depths alongthe collimator axis to achieve desired optical numerical apertures. Theholes of the collimators geometrically limit the viewing angle. Thetransmitting numeral aperture is decided by the thickness of thecollimator and the hole aperture. The holes may be filled with anoptically transparent material in some applications and may be void insome designs.

In implementations, the support substrate may be coated with one or moreoptical filter films to reduce or eliminate background light such as theIR light from the sunlight while transmitting desired light in apredetermined spectral band for the probe light that is used toilluminate the finger.

FIG. 27 shows an array of optical spatial filters coupled with microlens array where each microlens is located with respect to acorresponding through hole of an optical spatial filter so that eachunit collimator includes a micro lens and a micro spatial filter, suchas a micro hole. Each micro lens is structured and positioned to focusreceived light to the corresponding micro spatial filter without imagingthe received light. The micro hole limits the effective receivingnumerical aperture. The spatial filter may be printed on an opticallytransparent substrate, or etched on a piece of silicon wafer. The microlens array may be etched by MEMS processing or chemical processing. Themicro lens may also be made of a gradient refractive index material,e.g., cutting a piece of gradient refractive index glass fiber to aquarter pitch of length. The focal length of the micro lenses and thediameter of the spatial filter hole can be used to control thetransmitting numerical aperture of each unit. Like in other designs, thecollimator board may be coated with filter films to reduce or eliminatethe light band not used in the sensor such as the IR light from thesunlight.

FIG. 28 shows an example of an integrated CMOS photo detection arraysensor, with built-in collimation of light. The collimator is built bycombing an array of aligned holes 705 in different metal layers 704 andoxide layers 702,703 which are interleaved between metal layers toprovide separation. These holes can be aligned with photo sensitiveelements 701 in the optical sensor array. Optical fingerprint imager isimplemented with this integrated CMOS photo detection array sensor withbuilt-in collimation of light under the LCD display module 710 and coverglass. The fingerprint of the user's finger touch the sensor window areaof the cover glass can be imaged by detection of the light reflected offthe fingerprint valley and ridges. The light from a fingerprint ridgearea would be reduced, because the light is absorbed in fingerprinttissue at the ridge area while the light from the fingerprint valleyarea stronger by comparison. This difference in the light levels betweenthe ridges and valleys of a fingerprint produces a fingerprint patternat the optical sensor array.

In the above optical sensor module designs based on collimators, thethickness or length of each collimator along the collimator can bedesigned to be large to deliver imaging light to a small area on theoptical detector array or to be small to deliver imaging light to alarge area on the optical detector array. When the thickness or lengthof each collimator along the collimator in a collimator array decreasesto a certain point, e.g., tens of microns, the field of the optical viewof each collimator may be relatively large to cover a patch of adjacentoptical detectors on the optical detector array, e.g., an area of 1 mmby 1 mm. In some device designs, optical fingerprint sensing can beachieved by using an array of pinholes with each pinhole having asufficiently large field of optical view to cover a patch of adjacentoptical detectors in the optical detector array to achieve a high imageresolution at the optical detector array in sensing a fingerprint. Incomparison with a collimator design, a pinhole array can have a thinnerdimension and a smaller number of pinholes to achieve a desired highimaging resolution without an imaging lens. Also, different from theimaging via optical collimators, imaging with the array of pinholes useseach pinhole as a pinhole camera to capture the image and the imagereconstruction process based on the pinhole camera operation isdifferent that by using the optical collimator array: each pinholeestablishes a sub-image zone and the sub image zones by differentpinholes in the array of pinholes are stitched together to construct thewhole image. The image resolution by the optical sensor module with apinhole array is related to the sensitive element size of the detectorarray and thus the sensing resolution can be adjusted or optimized byadjusting the detector dimensions.

A pinhole array can be relatively simple to fabricate based on varioussemiconductor patterning techniques or processes or other fabricationmethods at relatively low costs. A pinhole array can also providespatial filtering operation to advantageously reduce the amount of thebackground light that enters the photodetector array in the opticalsensor module. Similar to designing the optical sensor modules withoptical collimators, one or more optical filters may be provided in theoptical sensor module with a pinhole array to filter out the backgroundlight and to reduce the amount of the background light at thephotodetector array for improved optical sensing of the returned lightfrom the fingerprint sensing area due to the illumination by theillumination light generated for optical sensing. For example, the oneor more optical filters can be configured, for example, as bandpassfilters to allow transmission of the illumination light for opticalsensing while blocking other light components such as the IR light inthe sunlight. This optical filtering can be an effective in reducing thebackground light caused by sunlight when using the device outdoors. Theone or more optical filters can be implemented as, for example, opticalfilter coatings formed on one or more interfaces along the optical pathto the photodetector array in the optical sensor module or one or morediscrete optical filters.

In an optical sensor module based on optical collimators, the opticalimaging resolution at the optical sensor array can be improved byconfiguring the optical collimators in a way to provide a pinhole cameraeffect. FIG. 29 shows an example of such a design.

In FIG. 29, a collimator unit 618 of an array of such opticalcollimators guides the light from the corresponding detection area unitto the photo detector array 621. The aperture of the collimator unitforms a small field of view (FOV) 618 b. If the detector in the photodetector array 621 does not capture the details in each unit FOV, theimaging resolution is decided by the FOV of each collimator unit. Toimprove the detection resolution, the FOV of each collimator unit needsto be reduced. However, when a gap 618 a is provided between each photodetector in the photo detector array 621 and the correspondingcollimator 618, the small aperture of the collimator unit acts as apinhole. This pinhole camera effect provides a higher imaging resolutionin the image of each unit of FOV. When there are multiple detectorelements in a unit FOV, such as shown in the insert 621 a, the imagesdetails in the unit FOV can be recognized. This means that the detectionresolution is improved. In implementations, such a gap can be providedin various ways, including, e.g., adding optical filter films 618 abetween the collimators 618 and the optical sensor array 621.

With the help of the pinhole camera effect, the fill factor of thecollimator board, may be optimized. For example, to detect an area of 10mm×10 mm in size, if each unit FOV covers an area of 1 mm×1 mm, a 10×10collimator array can be used. If in each unit FOV the detector can get20×20 definition image, the overall detection resolution is 200×200, or50 micron, or 500 psi. This method can be applied for all types ofcollimator approaches.

FIG. 30 shows another example for using the pinhole camera effect toimprove the optical imaging resolution. In this example, the opticalsensor module includes several layers: a spacer 917, a pinhole array 617which may be an optical collimator array with a sufficiently smallthickness, a protection material 919, a photo detector array 621, and acircuit board 623. The object optical distance is decided by the totalmaterial thickness from sensing surface to the pinhole plane, includingthe optical thickness of the display module 433, the thickness of thespacer 917, any filter coating thickness, any air gap thickness, and anyglue material thickness. The image optical distance is decided by thetotal material thickness from the pinhole plane to the photo detectorarray, including the protection material thickness, any filter coatingthickness, any air gaps thickness, any glue material thickness. Theimage magnification is decided by the image optical distance comparingwith the object optical distance. The detection mode can be optimized bysetting a proper magnification. For example, the magnification may beset to be less than 1, such as, 0.7, or 0.5 etc. In some device designs,the spacer and the pinhole array layer may be combined into a singlecomponent. In other designs, the pinhole array and the protection layermay be combined to a single component so as to pre-define the centercoordinates of each pinhole.

FIG. 31 shows an example of the optical imaging based on the pinholecamera effect. On the object side, the whole detection zone 921 on theLCD display panel is divided into multiple sub-detection zones 923. Apinhole array 920 is provided for imaging the detection zone 921. Eachpinhole unit in the pinhole array 920 is responsible for a small fieldof view (FOV) 925. Each small FOV 925 covers a sub-detection zone 923.As shown in FIG. 31, each small FOV of one pinhole can overlap withsmall FOVs of its neighboring pinholes. On the image side, eachsub-detection zone 923 in the optical sensor array captures an image933. Also shown in FIG. 31, each small FOV 925 of a pinhole has acorresponding image zone 935. The magnification of this system can beoptimized so that the images of each sub-detection zone can beseparately distinguished. In other words, the images of the small FOVsdo not overlap each other. In this detection mode, the centralcoordinates of each pinhole are pre-defined and the image spotcoordinates of each LCD display pixel can be pre-calibrated and thispre-calibration may be used to generate a calibration table for thecalibration during the sensor operation. In this design, the image ofthe pinhole camera is inversed and the signal processing can recover thewhole image based on the calibration table.

In the above illustrated examples for optical collimators, the directionof the optical collimators for directing light from a finger on the topof the display screen into the optical sensor array for fingerprintsensing may be either perpendicular to the top touch surface of LCDdisplay screen to collect returned probe light from the finger forfingerprint sensing, a majority of which is in a light directionperpendicular to the top touch surface. In practice, when a touchedfinger is dry, the image contrast in the detected images in the opticalsensor array by sensing such returned probe light that is largelyperpendicular to the top touch surface is lower than the same imageobtained from returned probe light that is at an angle with respect tothe perpendicular direction of the top touch surface. This is in partbecause optical sensing of angled returned light spatially filters outthe strong returned light from the top touch surface that is mostlyperpendicular to the top touch surface. In consideration of this aspectof the optical sensing of the returned probe light from the top touchsurface, the optical collimators may be oriented so that the axis ofeach collimator unit may be slanted with respect to the top touchsurface as shown in the example in FIG. 22B.

In fabrication, however, it is more complex and costly to fabricateslanted collimators. One way to use perpendicular optical collimators asshown in FIGS. 20 and 21B while still achieving a higher contrast in theoptical sensing by selectively detecting angled returned light from thetop touch surface is to provide an optical deflection or diffractiondevice or layer between the perpendicular optical collimators and thereturned light from the top touch surface prior to entering theperpendicular optical collimators. This optical deflection ordiffraction device or layer can be, in some implementations, between theOLED display panel and the perpendicular optical collimators to selectonly returned probe light that is at some slanted angle to enter theperpendicular optical collimators for optical detection by the opticaldetector array on the other end of the perpendicular optical collimatorswhile blocking or reducing the amount of the returned probe light fromthe top touch surface that is perpendicular to the top touch surfacefrom entering the optical collimators. This optical deflection ordiffraction device or layer may be implemented in various forms,including, e.g., an array of prisms, an optical layer with a diffractionpattern, or other devices located between the optical collimators andthe display panel to select angled probe light returned from the displaypanel to enter the optical collimators while reducing an amount of thereturned probe light that is perpendicular to the display panel andenters the optical collimators.

FIG. 32 shows an example of an optical sensor module using an opticalpinhole array for optical sensing. As illustrated, an pinhole array 920a is formed between the LCD display module 433 and the optical photodetector array 621 to image the sensing area where finger 60 is pressedon onto the optical photo detector array 621.

The thickness T of the pinhole layers 920 a dictates the field of view(FOV) angles. Together with the distances from the sensing surface tothe pinhole array 920 a and from the image plane to the pinhole array920 a, the sensing area FOVs and imaging area FOVi are defined. Theimage magnification is given by Di/Ds, where Di is the thickness of theoptical transparent layer 919 a between the pinhole array 920 a and theoptical sensor array 621 and Ds is the thickness of the combined stackby the spacer 917, the LCD display module 433 and the top cover glasslayer 431. The device parameters such as the pinhole layer thickness T,Ds, and Di can be optimized for a desired combination of FOV and imagemagnification. For example, the optical sensor module can be configuredwith desired parameters to render the neighboring FOVs of correspondingneighboring pinholes in the array 920 a to properly overlap if sodesired. Similarly, the neighboring FOVi can also be adjusted to beoverlapped or fully separated as discrete FOVi. In an optical sensormodule designed to cause neighboring FOVs to overlap each other, some ofthe spots on the sensing surface can have multiple image spots. Thissignature can be used to enhance the detection.

In the example in FIG. 32, optical filter films for reducing thebackground light may be formed or coated on the spacer 917, on thepinhole layers 920 a, on the protection 919 a, or on the displaysurfaces. As illustrated in the figure, when background light 937 isprojected onto the finger tissues 60, short wavelength component aremostly absorbed, partial long wavelength (such as red light or infraredlight) light is transmitted towards the detector 621. The optical filterfilms can be used to reject those long wavelength components to improvethe detection of returned light signals that carry the fingerinformation.

FIGS. 33A and 33B show an example of an optical fingerprint senor undera LCD display panel having an optical deflection or diffraction deviceor layer.

As shown in FIG. 33A, each collimator 2001 in the collimator array maybe an extended channel along an axis vertical or perpendicular to thedisplay surfaces. A viewing angle adaptor optical layer 2210 is used toadjust the viewing angle of the returned probe light from the displaypanel and is located between the optical collimators 2001 and the LCDdisplay panel to select angled probe light returned from the displaypanel to enter the optical collimators 2001 while reducing an amount ofthe returned probe light that is perpendicular to the display panel andenters the optical collimators 2001.

FIG. 33B shows more details of the viewing angle adaptor optical layer3210 and the major probe light paths. For example, the viewing angleadaptor optical layer 3210 may be implemented as a diffraction patternlayer such as a prism structure 3210 a. Only the returned probe light 82a and 82 b from the finger with proper incident angles out of thedisplay panel can be bent to transmit through the collimator 2001. Incomparison, the returned probe light that is perpendicular to thedisplay panel is directed by the viewing angle adaptor optical layer2210 to be away from the original direction that is perpendicular to thedisplay panel and thus becomes off-axis incident light to the opticalcollimator 2001. This reduces the amount of the returned probe lightthat is perpendicular to the display panel and that can enter theoptical collimator 2001.

When the viewing angle is adjusted properly, the receiving light fromdifferent locations 63 a and 63 b of the fingerprint valley carries thefingerprint information. For example, under same illumination, light 82a may be stronger than light 82 b because of the viewing angel and thefingerprint profiles of the fingertip skin. This design allows theoptical sensor module to obtain some level of fingerprint shade. Thisarrangement improves the detection when the finger is dry.

In designing optical sensor modules under LCD display modules, varioustechnical features or properties of LCD display modules should beconsidered and factored into the overall optical sensor module designsto improve the optical sensing operation. The following sectionsdescribed several design examples.

One common component in various LCD display modules is a light diffuserwhich may a sheet that diffuses the incident light to differentdirections to achieve a large viewing angle and the spatial uniformityof the display. The presence of this LCD diffuser layer, however, candegrade the optical detection by the under-LCD optical sensor module.

FIGS. 34A and 34B show a LCD light diffuser layer 433 b located betweenthe LCD waveguide layer 433 c and other LCD layers 433 a. In some LCDassemblies, the cover glass layer 431 may be separated by a distancefrom the underlying diffuser sheet 433 b (e.g., several millimeters insome LCD devices), and the optical collimator array 617 is separatedfrom the diffuser sheet 433 b by the light waveguide board 433 c (whichmay be sub mini-meters thick). Under this structure, the strongdiffusion in the diffuser sheet 433 b can significantly reduce thesignal contrast in the signal light that passes through the LCD displaymodule 433 to reach the optical detector array 621. The light diffusionat the LCD diffuser layer 433 b, although desirable for displayoperations, degrades the fingerprint detection performance.

This undesired effect of the LCD diffuser layer 433 b may be mitigatedby using different techniques. Two examples are illustrated in FIGS. 34Aand 34B.

FIG. 34A shows one example in which holes 951 a can be made in thecorresponding area or all over the diffuser sheet 433 b in the LCDdisplay module in the section of the diffuser sheet 433 b above theoptical sensor module to improve the transmission of the returned lightfrom the top cover glass 431 to the optical detector array 621. The holesizes, shapes and distribution can be selected based on the specificdesign needs. For example, the hole size may be larger than the probelight wave lengths so as to avoid strong diffraction. For example, acollimator unit aperture may be about 40 micron in diameter and thediffuser sheet hole size may be 5 micron, 10 micron, 30 micron, 40micron, or 100 micron and so on. The inclusion of the holes 951 a in theLCD diffuser layer 433 b in this design is to establish a light path foreach of the collimator unit. Each collimator unit aperture may have oneor multiple holes in the diffuser sheet to provide a desired light pathfrom the top cover glass 431 to the optical detector array 621. If thecollimator unit apertures are discrete with a relatively large pitchdistance (for example 1 mm or so), the holes in the diffuser sheet maybe drilled with the same pitch distance. The non-uniformity in thedetection can be calibrated.

FIG. 34B shows another example where the diffuser sheet can bestructured to include low diffusion optical transparent spots 951 bwhere the light diffusion is weak in the region above the optical sensormodule to improve the transmission of the light to the optical sensormodule. The transparent spot sizes, shapes and distribution e can beselected based on the specific design needs. For example, the hole sizemay be larger than the probe light wave lengths so as to avoid strongdiffraction, and the spot distribution be such that each collimator unithas one or more transparent light paths to allow efficient reception ofthe returned light from the top cover glass 431 through the LCD displaylayers. If the collimator unit apertures are discrete with large pitchdistance (for example 1 mm or so), the transparent spots in the diffusersheet may be made with the same pitch distance. If the diffuser sheet ismade of a rough surface material that diffracts or diffuses light, aselected material can be selectively applied to the rough surface toprovide some transparent material to reduce the original opticaldiffusion of the rough surface. Examples for suitable materials includeepoxy, wax, or oil and can effectively modify the diffusion.

For a given LCD diffuser layer, a long wavelength light source may beselected to generate the probe or illumination light so that thediffuser scattering for such light is weak so that more light can passthrough the diffuser layer to reach the optical sensor module.

For another example, referring to FIGS. 35A and 35B, various LCD displaymodules include an optical reflector layer or film 433 d in LCD belowthe LCD waveguide layer 433 c to reflect the unused light back to theLCD layers for enhancing the display brightness. However, the presenceof this optical reflector film 433 d can block most of the light fromreaching the optical sensor module under the LCD and thus can adverselyaffect the optical fingerprint sensing. This optical reflector layer canbe modified in a way that maintains the desired optical reflection underthe LCD waveguide layer in most locations while allowing for desiredoptical transmission at the location of the under-LCD optical sensormodule. In some implementations, the collimator module 617 for theoptical sensor under the LCD can be fixed to touch the reflector film433 d.

FIG. 34C shows another example for providing transparent light paths forguiding light from one or more illumination light sources 436 to improvethe fingerprint sensing of the detection module without significantdiffusion by the diffusion layer. For example, holes 969 may beselectively formed in the light diffuser film 433 b to improve lighttransmission to the under-LCD optical fingerprint sensor. To avoid theinfluence of the display performance, the light path holes may be tiltedto maintain some level of light diffusion function in the area of theholes 969. In addition, such holes 969 may be designed to be small,e.g., 0.3 mm or less, to further enhance diffusion of the backlightingwhile still providing improved optical imaging at the under-LCD opticalfingerprint sensor. In implementations, the light path holes may beempty with air, may be filled with a transparent material.

In some designs, the light path holes 969 may not be limited at acertain area but may be distributed all over the light diffuser film 433b, e.g., the holes 969 may be evenly distributed in the entire film 433b. This design eliminates the undesired spatial non-uniform illuminationcreated by the selected holes 969 in certain area but not in otherareas. In some designs, the light path holes 969 may be distributed in aspatial gradient pattern so that any change in the LCD illuminationcaused by the holes 969 would be gradual and less visible.

FIG. 35A shows one example for modifying the optical reflector layer byincluding or forming light-transmitting holes in the region of theoptical sensor module location in the optical reflector film to allowoptical reflection for LCD display in most parts of the opticalreflector film while providing the optical collimator array 617 withtransparent light paths for receiving light reflected from the finger ontop of the LCD. The hole sizes, shapes and distribution can beconfigured to meet the needs of optical sensing. For example, the holesize may be larger than the probe light wave lengths so as to avoidstrong diffraction. For example, the collimator unit aperture may bearound 40 micron in diameter and the diffuser sheet hole size may be 5micron, 10 micron, 30 micron, 40 micron, or 100 micron and so on. Eachcollimator unit aperture may have one or multiple holes in the opticalreflector layer to provide desired light paths for optical sensing. Thenon-uniformity in the detection can be calibrated. If the collimatorunit apertures are discrete with large pitch distance (for example 1 mmor so), the holes in the reflector film may be drilled with the samepitch distance.

FIG. 35B shows another example for modifying the optical reflector layerin the LCD in which the optical reflectance of the optical reflectorfilm may be modified to allow for some degree of optical transmissionfor optical sensing by the underlying optical sensor. Various commercialLCD reflector films use flexible plastic material as substrate and theoptical transmittance of such plastic materials may be sufficient fortransmitting sufficient light to the optical sensor module forfingerprint sensing.

In the above designs for the LCD diffuser layer and LCD reflector layer,the holes may be formed in a region where the one or more illuminationlight sources are located to allow sufficient transmission of theillumination light to pass through the LCD display module layers toreach the top cover glass for illuminating a finger for the opticalsensing operation.

In the above designs, the optical sensor module is located underneaththe LCD display module and thus is under the LCD waveguide layer whichis designed to guide the backlighting light from the backlighting lightsource to the LCD display area. As shown in FIG. 36, the backlightinglight from the display light sources 434 (e.g., LEDs) is guided by thewaveguide 433 c and is diffused by the LCD diffuser layer to leave thewaveguide 433 c to provide the needed backlighting for the LCD. Thelight may be uniformly leaked from one side surface of the waveguide 433c and is then diffused by the diffuser sheet 433 b. In some LCDs, abouthalf of the diffused light 957 may propagate towards the collimator 617and becomes strong background light in the optical sensing detection.

One or more extra light sources 436 can be provided in connection withthe optical sensor module: to illuminate the finger and to provide thelight carrying the fingerprint pattern information to the optical sensormodule underneath the LCD. Due to the location of the illumination lightsources 436 (e.g., below the reflector film 433 d next to or adjacent tothe optical sensor), the light guide function of the waveguide 433 c isnot effective to the light from the illumination light sources 436 sothat the light from the 436 can be more efficiently reach the topsurface of the LCD panel for illuminating a finger.

In addition, the illumination light sources 436 can be designed to emitillumination at one or more optical wavelengths different from the LCDdisplay illumination light wavelengths from the LCD display backlightinglight sources 434. The illumination light sources 436 can be used forboth fingerprint sensing and other sensing functions.

The above design for selecting the illumination light at one or moreoptical wavelengths that are different from the optical wavelength ofthe backlighting light for the LCD display may be used to reduce powerconsumption. Using the display backlighting light sources for thefingerprint detection requires the display backlighting light sources tobe turned on for performing optical fingerprint sensing. This designconsumes more power when compared to the above design where theillumination light for optical sensing is different from thebacklighting light in optical wavelength in part to allow for opticalsensing operation without turning on the LCD backlighting light. Theabove design for selecting the illumination light at one or more opticalwavelengths that are different from the optical wavelength of thebacklighting light for the LCD display enables flexible selection of theillumination light sources to gain additional advantages. For example,infrared light can be used as the illumination sources 436 so that theLCD diffuser layer becomes more transparent to the IR illumination lightfor desired higher transmission of the IR illumination light. Foranother example, the illumination light sources can be selected toprovide multiple wavelengths for other functions such as anti-spoofliveness sensing, heartbeat sensing etc.

In designing an optical sensor module under LCD, the locations andspatial distribution of the illumination light sources 436 can be usedto adjust the observing angle so as to optimize the sensing quality.

In placing an optical sensor module under a LCD module, additionaloptical designs may be used to enhance the delivery of the backlightinglight from the waveguide layer into the LCD layers while maintainingsufficient delivery of the illumination light for optical sensing to theoptical sensor module.

FIGS. 37A-37D show examples of enhancement structures that includes twoor more layers of back light enhancement films such as 433 px and 433 pyas part of the LCD layer structure shown as 433 a. The back lightenhancement films 433 px and 433 py are formed on top of the lightdiffuser layer 433 b.

In the example in FIG. 37A, each of the enhancement films 433 px and 433py includes a polarized prism structure. The prism groove directions ofthe two enhancement films 433 px and 433 py are substantiallyperpendicular to each other to collectively form a pair of enhancementfilms to improve delivery of the illumination light to the LCD panel.However, this function of the enhancement films may adversely affectoptical imaging of the under-LCD optical fingerprint sensor module 621Uif not properly configured.

As shown in the examples in FIGS. 37B and 37C, the extra light sourceillumination direction and the detector viewing direction can bespecifically configured not to be along the prism groove directions ofthe enhancement films 433 px and 433 py to reduce the adverse imagingimpact of the enhancement films for optical fingerprint sensing. Thisdesign is to get a clear image without punch holes in the enhancementfilms. The viewing angle ϕ1 and the illumination angle ϕ2 should beadjusted according to the design of the enhancement films.

The example in FIG. 37D shows a particular design of the collimator unit617U and a photodetector array unit 621U. The collimator unit 617U isused to provide an imaging function that is realized by a micro lens,pinholes or a combination of a micro lens and pinholes. A larger sensingarea at the photodetector array unit 621U can be realized by optimizingthe single detection unit design or by using multiple detection units.

FIG. 38 shows an example of a light waveguide layer in the LCD module toinclude a partially transparent section in the detection light paths toallow for improve optical transmission of the illumination light foroptical sensing to pass through the waveguide layer.

FIGS. 39A-39C show examples for designing an illumination light sourcefor the optical sensing in an optical sensor module under the LCDdisplay module. In a LCD display module, the optical reflector layerenhance the LCD display brightness by recycling unused backlightinglight back to the LCD layers. In this regard, a defect in the opticalreflectivity along the optical reflector film, e.g., a mechanical defectin the reflector film, can cause a visible change in the brightness ofthe LCD display and thus is undesirable. FIGS. 39A-39C illustrate designfeatures for reducing the adverse effect of defects in the reflectorlayer or film.

As shown in FIG. 39A, micro holes 973 can be provided in the reflectorlayer 433 d at the location of the illumination light sources 436 forthe visible light component in the illumination light. This visiblelight component is used to provide illumination in a limited area of thedisplay to show essential text or sign information without turning onthe display back light.

As shown in FIG. 39B, another solution is to select the illuminationlight source wavelengths to be out of the reflector film's working bandwhich is generally in the visible band. The illumination light sources436 for optical sensing may be outside the reflection spectral range ofthe reflector film, e.g., short wavelength range below 400 nm (e.g., 380nm) or long wavelength range beyond the visible red range (e.g., 780 nm,900 nm, 940 nm, etc.) so that the illumination light can pass throughthe reflector film or layer without the need to form holes in thereflector film.

FIG. 39C shows yet another design solution that designs the reflectorfilm to include a narrow band transmission window 975 for transmittingthe illumination light for optical detection. For example, this narrowtransparent or transmission window in the reflector film may be between525 nm and 535 nm.

Portable devices such as mobile phones or other devices or systems basedon the optical sensing disclosed in this document can be configured toprovide additional operation features.

For example, the LCD display panel can be controlled to provide a localflash mode to illuminate the fingerprint sensing area by operatingselected LCD display pixels underneath the sensing area. This can beprovided in an optical sensor module under the LCD display panel, e.g.,FIGS. 4A and 4B based on an optical imaging design or FIGS. 21A and 21Bbased on optical imaging via an optical collimator array. In the eventof acquiring a fingerprint image, the LCD display pixels in the sensingwindow area and the illumination light sources can be turned onmomentarily to produce high intensity illumination for optical sensingof a fingerprint, and, at the same time, the photo detection sensorarray 621 is turned on to capture the fingerprint image in sync with theturning on of the illumination light. The time to turn on theillumination light can be relatively short but the emission intensitycan be set to be high. For this reason, this mode for opticalfingerprint sensing is a flash mode that enable the photo detectorsensor array 621 to detect a larger amount of light to improve the imagesensing performance.

The optical sensors for sensing optical fingerprints disclosed above canbe used to capture high quality images of fingerprints to enablediscrimination of small changes in captured fingerprints that arecaptured at different times. Notably, when a person presses a finger onthe device, the contact with the top touch surface over the displayscreen may subject to changes due to changes in the pressing force. Whenthe finger touches the sensing zone on the cover glass, changes in thetouching force may cause several detectable changes at the opticalsensor array: (1) fingerprint deforming, (2) a change in the contactingarea, (3) fingerprint ridge widening, and (4) a change in the blood flowdynamics at the pressed area. Those changes can be optically capturedand can be used to calculate the corresponding changes in the touchforce. The touch force sensing adds more functions to the fingerprintsensing.

Referring to FIG. 40, the contact profile area increases with anincrease in the press force, meanwhile the ridge-print expands with theincrease in the press force. Conversely, the contact profile areadecreases with an decrease in the press force, meanwhile the ridge-printcontracts or shrinks with the decrease in the press force. FIG. 40 showstwo different fingerprint patterns of the same finger under differentpress forces: the lightly pressed fingerprint 2301 and the heavilypressed fingerprint 3303. The returned probe light from a selectedintegration zone 3305 of the fingerprint on the touch surface can becaptured by a portion of the optical sensors on the optical sensor arraythat correspond to the selected integration zone 3305 on the touchsurface. The detected signals from those optical sensors are analyzed toextract useful information as further explained below.

When a finger touches the sensor surface, the finger tissues absorb thelight power thus the receiving power integrated over the photo diodearray is reduced. Especially in the case of total inner reflection modethat does not sense the low refractive index materials (water, sweatetc.), the sensor can be used to detect whether a finger touches thesensor or something else touches the sensor accidentally by analyzingthe receiving power change trend. Based on this sensing process, thesensor can decide whether a touch is a real fingerprint touch and thuscan detect whether to wake up the mobile device based on whether thetouch is a real finger press. Because the detection is based onintegration power detection, the light source for optical fingerprintsensing at a power saving mode.

In the detailed fingerprint map, when the press force increases, thefingerprint ridges expands, and more light is absorbed at the touchinterface by the expanded fingerprint ridges. Therefore within arelatively small observing zone 3305, the integrated received lightpower change reflects the changes in the press force. Based on this, thepress force can be detected.

Accordingly, by analyzing the integrated received probe light powerchange within a small zone, it is possible to monitor time-domainevolution of the fingerprint ridge pattern deformation. This informationon the time-domain evolution of the fingerprint ridge patterndeformation can then be used to determine the time-domain evolution ofthe press force on the finger. In applications, the time-domainevolution of the press force by the finger of a person can be used todetermine the dynamics of the user's interaction by the touch of thefinger, including determining whether a person is pressing down on thetouch surface or removing a pressed finger away from the touch surface.Those user interaction dynamics can be used to trigger certainoperations of the mobile device or operations of certain apps on themobile device. For example, the time-domain evolution of the press forceby the finger of a person can be used to determine whether a touch by aperson is an intended touch to operate the mobile device or anunintended touch by accident and, based on such determination, themobile device control system can determine whether or not to wake up themobile device in a sleep mode.

In addition, under different press forces, a finger of a living personin contact with the touch surface can exhibit different characteristicsin the optical extinction ratio obtained at two different probe lightwavelengths as explained with respect FIGS. 14 and 15. Referring back toFIG. 40, the lightly pressed fingerprint 3301 may not significantlyrestrict the flow of the blood into the pressed portion of the fingerand thus produces an optical extinction ratio obtained at two differentprobe light wavelengths that indicates a living person tissue. When theperson presses the finger hard to produce the heavily pressedfingerprint 3303, the blood flow to the pressed finger portion may beseverely reduced and, accordingly, the corresponding optical extinctionratio obtained at two different probe light wavelengths would bedifferent from that of the lightly pressed fingerprint 3301. Therefore,the optical extinction ratios obtained at two different probe lightwavelengths vary under different press forces and different blood flowconditions. Such variation is different from the optical extinctionratios obtained at two different probe light wavelengths from pressingwith different forces of a fake fingerprint pattern of a man-madematerial.

Therefore, the optical extinction ratios obtained at two different probelight wavelengths can also be used to determine whether a touch is by auser's finger or something else. This determination can also be used todetermine whether to wake up the mobile device in a sleep mode.

For yet another example, the disclosed optical sensor technology can beused to monitor the natural motions that a live person's finger tends tobehave due to the person's natural movement or motion (either intendedor unintended) or pulsing when the blood flows through the person's bodyin connection with the heartbeat. The wake-up operation or userauthentication can be based on the combination of the both the opticalsensing of the fingerprint pattern and the positive determination of thepresence of a live person to enhance the access control. For yet anotherexample, the optical sensor module may include a sensing function formeasuring a glucose level or a degree of oxygen saturation based onoptical sensing in the returned light from a finger or palm. As yetanother example, as a person touches the display screen, a change in thetouching force can be reflected in one or more ways, includingfingerprint pattern deforming, a change in the contacting area betweenthe finger and the screen surface, fingerprint ridge widening, or ablood flow dynamics change. Those and other changes can be measured byoptical sensing based on the disclosed optical sensor technology and canbe used to calculate the touch force. This touch force sensing can beused to add more functions to the optical sensor module beyond thefingerprint sensing.

While this patent document contains many specifics, these should not beconstrued as limitations on the scope of any invention or of what may beclaimed, but rather as descriptions of features that may be specific toparticular embodiments of particular inventions. Certain features thatare described in this patent document in the context of separateembodiments can also be implemented in combination in a singleembodiment. Conversely, various features that are described in thecontext of a single embodiment can also be implemented in multipleembodiments separately or in any suitable subcombination. Moreover,although features may be described above as acting in certaincombinations and even initially claimed as such, one or more featuresfrom a claimed combination can in some cases be excised from thecombination, and the claimed combination may be directed to asubcombination or variation of a subcombination.

Similarly, while operations are depicted in the drawings in a particularorder, this should not be understood as requiring that such operationsbe performed in the particular order shown or in sequential order, orthat all illustrated operations be performed, to achieve desirableresults. Moreover, the separation of various system components in theembodiments described in this patent document should not be understoodas requiring such separation in all embodiments.

Only a few implementations and examples are described and otherimplementations, enhancements and variations can be made based on whatis described and illustrated in this patent document.

What is claimed is:
 1. An electronic device capable of detecting afingerprint by optical sensing, comprising: a liquid crystal display(LCD) screen that provides touch sensing operations and includes a LCDdisplay panel structure to display images; a top transparent layerformed over the device screen as an interface for being touched by auser for the touch sensing operations and for transmitting the lightfrom the display structure to display images to a user; and an opticalsensor module located below the display panel structure to receive probelight that passes through the LCD screen to detect a fingerprint,wherein the LCD display panel structure includes a selected region thatis located above the optical sensor module and is structured differentlyfrom other regions in the LCD display panel structure so as to transmitmore probe light than the other regions in the LCD display panelstructure to increase an amount of the received probe light at theoptical sensor module.
 2. The device as in claim 1, wherein: the toptransparent layer includes a designated fingerprint sensing region for auser to touch with a finger for fingerprint sensing; the optical sensormodule below the display panel structure includes a transparent block incontact with the display panel substrate to receive light from the LCDdisplay panel structure and returned from the top transparent layer,wherein the optical sensor module is positioned relative to thedesignated fingerprint sensing region and structured to selectivelyreceive returned light from the top surface of the top transparent layerwhen in contact with a person's skin.
 3. The device as in claim 1,wherein: the LCD display panel structure includes a light diffuser layerthat diffuses light and the light diffuser includes holes at theselected area within the LCD display panel structure above the opticalsensor module to allow more probe light to be transmitted to reach theoptical sensor module than other areas in the light diffuser layer. 4.The device as in claim 1, wherein: the LCD display panel structureincludes a light diffuser layer that diffuses light and the lightdiffuser layer includes a special diffuser region in the selected areawithin the LCD display panel structure above the optical sensor modulethat diffuses light less than other parts of the light diffuser layer toallow more probe light to transmit through to reach the optical sensormodule than other areas in the light diffuser layer.
 5. The device as inclaim 1, comprising: LCD illumination light sources to providebacklighting to the LCD display panel structure for displaying images;an optical reflector layer formed on a bottom region of the LCD displaypanel to reflect light back to the LCD display panel structure; andholes formed in only one region of the optical reflector layer that islocated in the selected area within the LCD display panel structureabove the optical sensor module to allow light to be transmitted toreach the optical sensor module.
 6. The device as in claim 1,comprising: LCD illumination light sources to provide backlighting tothe LCD display panel structure for displaying images; an opticalreflector layer formed on a bottom region of the LCD display panel toreflect light back to the LCD display panel structure, wherein theoptical reflector layer includes a selected region that is lessreflective than other regions of the optical reflector layer and islocated above the optical sensor module to allow light to be transmittedto reach the optical sensor module.
 7. An electronic device capable ofdetecting a fingerprint by optical sensing, comprising: a liquid crystaldisplay (LCD) screen that provides touch sensing operations and includesa LCD display panel structure to display images; a top transparent layerformed over the device screen as an interface for being touched by auser for the touch sensing operations and for transmitting the lightfrom the display structure to display images to a user, the toptransparent layer includes a designated fingerprint sensing area forfingerprint sensing in addition for viewing the images by the LCDdisplay panel structure; an optical sensor module located below thedisplay panel structure to receive probe light that passes through theLCD screen to detect a fingerprint; LCD illumination light sources toprovide backlighting to the LCD display panel structure for displayingimages; one or more probe light sources formed under the LCD displaypanel structure to project the probe light to pass through the LCDdisplay panel structure and configured to illuminate the designatedfingerprint sensing area to be visibly different from a surrounding areaand other areas of the top transparent layer and to further illuminatean object or finger on top of or in touch with the designate fingerprintsensing area of the top transparent layer above the LCD display panelstructure to cause reflected probe light from the illuminated object orfinger towards the optical sensor module for optical fingerprintsensing; and a device electronic control module coupled to the displaypanel structure to supply power to the one or more probe light sourcesand to control the LCD illumination light sources and the backlightingto the LCD display panel structure, and to turn on the one or more probelight sources to illuminate the designated fingerprint sensing areawhile turning off the LCD illumination light sources for thebacklighting to the LCD display panel structure in a sleep mode, andwherein the device electronic control module is configured to wake upthe LCD display panel structure from the sleep mode by turning on theLCD illumination light sources to provide the backlighting to the LCDdisplay panel structure when the optical sensor module detects thepresence of a person's skin at the designated fingerprint sensing regionof the top transparent layer under illumination by the one or more probelight sources only.
 8. The device as in claim 7, wherein: the deviceelectronic control module is configured to operate one or more probelight sources to intermittently emit the probe light, while turning offpower to the LCD display panel structure, when the LCD display panelstructure is in the sleep mode, to direct the intermittently probe lightto the designated fingerprint sensing region of the top transparentlayer for monitoring whether there is a person's skin in contact withthe designated fingerprint sensing region for waking up the device fromthe sleep mode.
 9. The device as in claim 8, wherein: the one or moreprobe light sources emit invisible light.
 10. The device as in claim 1,further comprising: a device electronic control module that grants auser's access to the device if a detected fingerprint matches afingerprint an authorized user.
 11. The device as in claim 10, wherein:the optical sensor module is configured to, in addition to detectingfingerprints, also detect a biometric parameter different from afingerprint by optical sensing to indicate whether a touch at the toptransparent layer associated with a detected fingerprint is from a liveperson, and the device electronic control module is configured to granta user's access to the device if both (1) a detected fingerprint matchesa fingerprint an authorized user and (2) the detected biometricparameter indicates the detected fingerprint is from a live person. 12.The device as in claim 11, wherein: the biometric parameter includes aheartbeat.
 13. The device as in claim 11, further comprising a biometricsensor that is separate from the optical sensor module and detects abiometric parameter different form a fingerprint to indicate whether atouch at the top transparent layer associated with a detectedfingerprint is from a live person, and wherein the device electroniccontrol module is configured to grant a user's access to the device ifboth (1) a detected fingerprint matches a fingerprint an authorized userand (2) the detected biometric parameter indicates the detectedfingerprint is from a live person.
 14. The device as in claim 1,comprising: a device electronic control module coupled to the opticalsensor module to receive information on multiple detected fingerprintsobtained from sensing a touch of a finger, wherein the device electroniccontrol module measures a change in the multiple detected fingerprintsand determines a touch force that causes the measured change.
 15. Thedevice as in claim 14, wherein: the change includes a change in thefingerprint image due to the touch force, a change in the touch area dueto the touch force, or a change in spacing of fingerprint ridges. 16.The device as in claim 1, wherein the device is a smartphone.
 17. Thedevice as in claim 1, wherein the device is a portable device.
 18. Thedevice as in claim 1, wherein the optical collimators are configured tocollect the returned light from the LCD display panel structure and toseparate light from different locations in the top transparent layerwhile directing the collected returned light to the optical sensorarray.
 19. The device as in claim 1, wherein: the optical sensor moduleincludes an optical collimator array of optical collimators thatreceives the probe light and an optical sensor array of optical sensorsto receive the probe light from the optical collimator array, and theoptical collimators include a substrate having an array of through holesformed in the substrate as the optical collimators.
 20. The device as inclaim 1, wherein: the optical sensor module includes an opticalcollimator array of optical collimators that receives the probe lightand an optical sensor array of optical sensors to receive the probelight from the optical collimator array, and the optical collimatorsinclude an array of optical waveguides or optical fibers.
 21. The deviceas in claim 1, wherein: the optical sensor module includes an opticalcollimator array of optical collimators that receives the probe lightand an optical sensor array of optical sensors to receive the probelight from the optical collimator array, and the optical collimatorsinclude a micro lens array of micro lenses and each micro lens focusreceived light without imaging the received light.
 22. An electronicdevice capable of detecting a fingerprint by optical sensing,comprising: a liquid crystal display (LCD) screen that provides touchsensing operations and includes a LCD display panel structure to displayimages; a top transparent layer formed over the device screen as aninterface for being touched by a user for the touch sensing operationsand for transmitting the light from the display structure to displayimages to a user; and an optical sensor module located below the displaypanel structure to receive probe light that passes through the LCDscreen to detect a fingerprint, wherein the optical sensor moduleincludes an optical collimator array of optical collimators thatreceives the probe light and an optical sensor array of optical sensorsto receive the probe light from the optical collimator array, wherein:the optical collimators include a micro lens array of micro lenses andeach micro lens focus received light without imaging the received light,the optical sensor module includes an array of optical filters that arespatially arranged to match the micro lenses of the micro lens array,one optical filter per one micro lens, and the optical filters filterthe light that reaches the optical sensor array.
 23. The device as inclaim 22, wherein: the optical sensor module includes an optical filterlayer shared by the optical collimators to filter the light that reachesthe optical sensor array.
 24. The device as in claim 1, wherein: theoptical sensor module includes an optical collimator array of opticalcollimators that receives the probe light and an optical sensor array ofoptical sensors to receive the probe light from the optical collimatorarray, and each optical collimator is structured to transmit light indirections along or close an axis of the optical collimator whileblocking light in other directions and to have a small transmissionnumeral aperture to achieve a high spatial resolution by the opticalcollimator array.
 25. The device as in claim 1, wherein: the LCD screenincludes a light diffuser layer that is configured to include a selectedlight diffuser layer area that is located in the selected region of theLCD display panel structure above the optical sensor module and includeslight transmission paths to allow reflected light from the toptransparent layer above the LCD screen to transmit through to reach theoptical sensor module.
 26. The device as in claim 1, wherein: the LCDdisplay panel structure includes LCD illumination light sources toprovide backlighting to the LCD display panel structure for displayingimages; and one or more probe light sources formed under the LCD displaypanel structure to project the probe light to pass through the LCDdisplay panel structure to illuminate a fingerprint sensor area on a topsurface of the top transparent layer to be distinct from a surroundingarea for the user to place a finger for optical fingerprint sensing. 27.The device as in claim 26, wherein: the LCD display panel structureincludes one or more backlight enhancement film layers each including anoptical polarized prism structure having two sets of prism grooves thatare perpendicular to each other; and the one or more probe light sourcesand the optical sensor module under the LCD display panel structure arearranged so that the optical sensor module receives the reflected probelight that is reflected from the top transparent layer and produced bythe one or more probe light sources at a direction that is differentfrom a direction of a prism groove.
 28. An electronic device capable ofdetecting a fingerprint by optical sensing, comprising: a liquid crystaldisplay (LCD) screen that provides touch sensing operations and includesa LCD display panel structure to display images; a LCD backlightinglight module coupled to the LCD screen to produce backlighting light tothe LCD screen for display images; a top transparent layer formed overthe device screen as an interface for being touched by a user for thetouch sensing operations and for transmitting the light from the displaystructure to display images to a user; an optical sensor module locatedbelow the LCD display panel structure to receive probe light that isreflected from the top transparent layer and passes through the LCDscreen to detect a fingerprint; one or more probe light sources,separate from the LCD backlighting light module, located under the LCDdisplay panel structure, to produce the probe light that passes throughthe LCD display panel structure to illuminate a designated fingerprintsensing area on the a top transparent layer to be visibly different froma surrounding area of the top transparent layer for a user to place afinger for optical fingerprint sensing; and a device control modulecoupled to the optical sensor module to process an output of the opticalsensor module to determine whether a detected fingerprint by the opticalsensor module matches a fingerprint an authorized user, in addition todetecting fingerprints, also detect a biometric parameter different forma fingerprint by optical sensing to indicate whether a touch at the toptransparent layer associated with a detected fingerprint is from a liveperson.
 29. The device as in claim 28, wherein: the one or more probelight sources produces the probe light at different optical wavelengthsso that the optical sensor module captures optical properties inreflected probe light by an object in contact with the designatedfingerprint sensing area on the top transparent layer at the differentoptical wavelengths, and the device control module is operable toprocess the captured optical properties in reflected probe light by theobject at the different optical wavelengths to determine whether theobject is a finger of a live person.
 30. The device as in claim 28,wherein: the LCD display panel structure includes a light diffuser layerthat diffuses light and the light diffuser includes holes at a selectedarea above the optical sensor module to allow light to be transmitted toreach the optical sensor module.
 31. The device as in claim 28, wherein:the LCD display panel structure includes a light diffuser layer thatdiffuses light and the light diffuser layer includes a selected areaabove the optical sensor module that diffuses light less than otherparts of the light diffuser layer to allow some light to transmitthrough to reach the optical sensor module.
 32. The device as in claim28, comprising: an optical reflector layer formed on a bottom region ofthe LCD display panel to reflect light back to the LCD display panelstructure; holes formed in a selected area above the optical sensormodule to allow light to be transmitted to reach the optical sensormodule.
 33. The device as in claim 28, wherein: the device controlmodule is configured to operate the one or more probe light sources tointermittently emit the probe light, while turning off power to the LCDdisplay panel structure, when the LCD display panel structure is in thesleep mode, to direct the intermittently probe light to the designatedfingerprint sensing region of the top transparent layer for monitoringwhether there is a person's skin in contact with the designatedfingerprint sensing region for waking up the device from the sleep mode.34. The device as in claim 28, wherein: the device control modulecoupled to the optical sensor module to receive information on multipledetected fingerprints obtained from sensing a touch of a finger, and thedevice control module measures a change in the multiple detectedfingerprints and determines a touch force that causes the measuredchange.
 35. The device as in claim 34, wherein: the change includes achange in the fingerprint image due to the touch force, a change in thetouch area due to the touch force, or a change in spacing of fingerprintridges.
 36. The device as in claim 28, wherein: the optical sensormodule includes an optical collimator array of optical collimators thatreceives the probe light and an optical sensor array of optical sensorsto receive the probe light from the optical collimator array, and theoptical collimators include a substrate having an array of through holesformed in the substrate as the optical collimators.
 37. The device as inclaim 28, wherein: the optical sensor module includes an opticalcollimator array of optical collimators that receives the probe lightand an optical sensor array of optical sensors to receive the probelight from the optical collimator array, and the optical collimatorsinclude an array of optical waveguides or optical fibers.
 38. The deviceas in claim 28, wherein: the optical sensor module includes an opticalcollimator array of optical collimators that receives the probe lightand an optical sensor array of optical sensors to receive the probelight from the optical collimator array, and the optical collimatorsinclude a micro lens array of micro lenses and each micro lens focusreceived light without imaging the received light.
 39. The device as inclaim 28, wherein: the LCD screen includes a light diffuser layer thatis configured to include a selected area that includes lighttransmission paths to allow reflected light from the top transparentlayer above the LCD screen to transmit through to reach the opticalsensor module.
 40. The device as in claim 28, wherein: the LCD displaypanel structure includes one or more backlight enhancement film layerseach including an optical polarized prism structure having two sets ofprism grooves that are perpendicular to each other; and the one or moreprobe light sources and the optical sensor module under the LCD displaypanel structure are arranged so that the optical sensor module receivesthe reflected probe light that is reflected from the top transparentlayer and produced by the one or more probe light sources at a directionthat is different from a direction of a prism groove.
 41. An electronicdevice capable of detecting a fingerprint by optical sensing,comprising: a liquid crystal display (LCD) screen that provides touchsensing operations and includes a LCD display panel structure to displayimages; a LCD backlighting light module coupled to the LCD screen toproduce backlighting light to the LCD screen to display images; a toptransparent layer formed over the LCD screen as an interface for beingtouched by a user for the touch sensing operations and for transmittingthe light from the display structure to display images to a user; anoptical sensor module located below the LCD panel structure to receivelight returned from the top transparent layer to detect a fingerprint,wherein the optical sensor module includes a transparent block incontact with the display panel substrate to receive the light from thedisplay panel structure, an optical sensor array that receives the lightand an optical imaging module that images the received light in thetransparent block onto the optical sensor array; and one or more probelight sources, separate from the LCD backlighting light module, locatedunder the LCD display panel structure, to produce the probe light thatpasses through the LCD display panel structure to illuminate adesignated fingerprint sensing area on the a top transparent layer to bevisibly different from a surrounding area of the top transparent layerfor a user to place a finger for optical fingerprint sensing.
 42. Thedevice as in claim 41, wherein the optical imaging module includes alens that images the received light in the transparent block onto theoptical sensor array.